If you get a chance to check out the June 2007 issue of Janes Defense Review p67-72 there is a story on the weight issues of the humvee and on the future of the project. Here are some highlights of the article to address some concerns raised here. I've put the parts in the article in quotes and italicized my own comments to give clarity/context to it.
"When it comes to describing the HMMWV, 'ubiquitous' seems insufficiently narrow...Ironically, perhaps, it is this success that has contributed to some of the system's greatest challenges...recent years have seen a great proliferation of tactical payload strain exacerbated by the mandates of add-on ballistic armour packages.
"LTC Samuel Honsey, US Army Project Manager for Light Tactical Vehicles, notes that the gross weight (GVW) rating of the M1114 is approximately 12,100 lbs, but 'they are rolling out of the gate at about 15,400 to 15,600 lbs' he says.
"LTC Honsey recently observed that the Humvee has become 'a zero sum game, ' with the addition of any new item mandating the remval of some existing element.
"The US is currently focusing its efforts in several arenas, including: expanded fielding of the latest enhancements to the Humvee; continuing the introduction of near-term and mid-term improvements to the current platform design; accelerated fielding of interim 'gapfiller' Mine Resistant Ambush Protection (MRAP) vehicles; and an emerging objective programme for a new vehicle known as the Joint Light Tactical Vehicle (JLTV)
"Current Humvee production efforts encompass the new M1151, M1152, and the M1165-series vehicles. The new platforms comprise a slant-back armament carrier, two-man armoured cab, and four-man armoured cab respectively."
Meaning that the M1114 as we know it is not being produced, but keep in mind the difference between a vehicle designation when talking about a humvee is usually subtle. The original difference between an M1025 and M1026 is a winch"Unlike the permanently up-armoured M1114-series, these three platforms were designed specifically for the application of additional armour packages over their base protection levels.
M1114s were originally sufficent to protect the soldier but the Army soon mandated new requirement to facilitate additional armor, issued out in what were known as "Frag kits""Three Frag Kits are currently being produced for the latest models. Frag Kit 1 covers the sides of the vehicle, minus the doors; Frag Kit 2 covers the frontal areas, and Frag Kit 5, the doors themselves. Frag Kits 3 and 4 have reportedly been developed but are not currently in production...[improvements] are constantly evolving and the recent features include a new fire-suppression system, improved air-conditioning, a new turret gunner restraint system, improved quick-release seat belts and an enhanced intercom system.
"Robert Gula, [senior vice-president of engineering and product development at AM General] also identifies a number of near-term Humvee improvements that will be incorporated into production over the next few months, including the new Objective Gunner's Protection Kit (O-GPK).
"Developed at the US Army's Picatinny [auto-censored]nal in New Jersey, the O-GPK...provides a motorised traversing operation (with battery backup), while safeguarding the gunner with a combinatino of greater protection and increased situational awareness.
Here is a picture of the O-GPK. The current official shield looks for the most part like this but without all of the ballistic glass 
"Gula goes on to highlight the overloading of the Humvees caused by the additional armour...'As the armour got improved and increased it just at up more payload. But the missions didn't change, so they still have the same amount of people, equipment and supplies to carry. And the end result is overloads.'
"He refers to a number of reliability enhancements implemented by AM General to address this problem, namely an improved frame (new higher-capacity construction), enhanced suspension (including springs, shocks, control arms and ball joints), improvements to the driveline, higher-capacity wheels and tyres, and improved engine cooling.
"Looking at beyond 2007, Gula highlights "further capability improvements in the vehicle that would raise the GVW to probably in the 16,000 - 17,000 range"
"These enhancements provide significantly improved crew space, creating room for communications equipment; offer improved maintainability with a much quicker engine-exchange process; provide enhanced electonics/diagnostics and further improved ballistic protection; and produce considerably increased engine power, while still running on JP-8. "And when you get done with all of that, the goal is, with all of the additional capability and armour weight, we will still get back to the same payload that an M1151, M1152 or M1165 had, befoer you put any armour on it," he says."
The article goes onto where the JLTV project stands and considering I just wrote probably the largest forum post on Armorama I will suggest you read the rest of the article. Gary, the article doesn't say much about the transmission so I hope what I gave helps in understanding.
As for those JLTV contract requirements, check this out
http://www.globalsecurity.org/military/systems/ground/jltv.htmJeff