Some information discovered in the National Archives:
The original proposal for the T28 heavy tank / T95 GMC in 1943 was:
75 gross tons
Frontal: 10" (254mm) basis
Sides: 8" (203mm) basis
Rear: 4ΒΌ" (107.95mm) basis
Roof & floor: 2" (50.8mm) thick
105mm Gun, 30 rounds
4 x M1919A4 MGs in external blisters (1,000 rds total)
So what caused the T28/T95 to bloat to 95-100 tons? (the exact weight is dependent on which reference you consult)
Well, they increased main gun stowage to 62 rounds of 105mm, and redesigned the armor scheme to provide frontal protection against tungsten carbide (HVAP / APCR) ammunition.
You'll love this next bit.
The Corps of Engineers were represented on the Ordnance Technical Committee; and assumed that the weight of the T28/T95 was to be 75-80 gross tons as in the original proposal; so they started to look at developing bridges to carry that amount of weight.
...Only nobody told them about the revised weight (95-100 tons) until the tanks were virtually complete.
EDIT: Added the crude photo of equally crude artwork included in the original 1943 proposal letter. You'll note that it's called just "A.T. Project".