What truck do you want to build?
Out of the box your kit builds into M925 - this truck has 10 wheels (duals on rear axles) and a winch.
If you want to build it as OIF M925 you need a set of new wheels, but no-one makes new pattern tires for 10-wheel 5-ton truck as used these days. The only replacement set for 10-wheel trucks is a set from Real Models, but these are old style tires, as those in the Italeri kit you have and they are no longer in use today.
You can also go different route and convert your truck to M925A2. This is a 6 wheel truck with significantly larger wheels and single wheels on rear axles. Several companies make wheels for A2 trucks. They call their sets "M923A2 wheels" or "M939A2 wheels", but it's all the same. Several manufacturers also make M923A1/M939A1 wheels, but for typical OIF truck you should use A2 wheels (A2 have CITS - central tire inflation system, while A1s don't have it). Some manufacturers call their wheels "Big Foot wheels", but in such case it is not clear if these are A1 or A2 type.
M939A2 wheels are available from Ordnance Models (OOP), CMK, Hobby Fan, Real Models, MR Modellbau and probably some others which I forgot. I would advise against CMK wheels - they are much too small and don't look right. They are smaller even than underscale wheels in Italeri M923A1 "Big Foot" kit... Ordnance wheels are flattened to represent the effect of the truck weight, but this is much overdone (and they are OOP).
Just note that to build your truck as A2 variant you need several other modifications, not just wheels. Some of them are described in my article about detailing Italeri kit (
http://vodnik2.republika.pl/pages/m923a1-mods/m923a1-mods.htm), but as I wrote about A1, there is at least one more change needed for A2 not mentioned in my text - different fuel tank.
And one more information - all those 5-ton trucks are officially known as M939 family. They are also commonly called "900" family.
M925, M925A1 and M925A2 are all cargo trucks with drop sides and with winch.
M923, M923A1 and M923A2 are identical to trucks listed above, but they don't have winch.
A"nothing" trucks have 10 wheels
A1 trucks have 6 larger wheels
A2 trucks have 6 larger wheels and CITS.
There are other differences between A"nothing", A1 and A2, but wheels are most noticeable.
Pawel