Hi Dave,
Looks like a nice clean build. I don't know much about US Shermans so I'll leave that to others.
Some observations on the finish; You could drill out the barrell a bit more or use gun metal to dull the inside down a bit (same detail on the MGs). The tracks are rubber and sould look a bit more grey rather than black. The headlights appear green? The top of the tank is very clean no dust or oil marks so you could dirty it up a bit with some Mig pigments. The tools on the US vehicles were OD the same as the tank, gun metal would be a better colour for the steel. Try using a lead pencil to highlight some of the areas that might get worn through normal wear and tear. You could put a small black wash around the petrol caps and add some dust into the tracks.
You have the makings of a very nice vehicle here that with a little more work would look great.
If you going to show it with the drivers hatches closed you need to add some periscopes.
Dave aka 'Gumpyoldman' did a good article on the M4 which gives a lot of tips and hints that will help you get a better vehicle. (see Features). There's a lot that you can add to the basic vehicle that with a bit of practice wll make a big difference. If this is your first one and as there is no stowage try adding some welds as per Dave's article, it's much easier than it seems.
Thanks for sharing and don't take this the wrong way OK - I made all these errors and a lot more on my lot LOL, LOL.
Cheers
Al