why isnt there much mention about bolting the t5s to a 248? Also if the t5s arent great for a 3/4 ton then which trannies are?
The T5 is probably the most economical transmission to swap. Economical in that the transmissions don't cost too much, and give 5 forward gears. If you routinely haul heavy loads, or have a big hp big torque motor, the t5 isn't the best transmission.
As mentioned by Longbox above, the MY6 (A833) 4 speed is agood transmission to put in a 3/4 ton.
Complete overkill for a 248 would be a NV4500 5 speed. This transmission has a granny low and an OD, and will work with a combined vehicle weight of 14000 lbs or more.
I have a NV4500 in a 59 1/2 ton with v8, and another one ready to go into a 1940 gmc 3/4 ton with 302 6 cylinder. They are sweet transmissions, but on the pricier side as in $1400 or more to swap in used transmission, and about $2500-3000 for a new swap.
As far as a T5 and a 248... The 248 uses the same bellhousing as a chevy 235. Everything you have read about swapping a t5 in a chevy will cross directly over to the 248 gmc. In the case of your 1954, the transmission will almost bolt directly up to your bellhousing. I believe you might have to extend the splines on the input shaft, and hog out the holes on the mounting ears.
An MY6 (A833) swap will require some precision machine work to mate up to your bellhousing. Either the bellhousing has to be bored out to 5.125 inches, or the bearing retainer has to be machined down to 4.686 inches to fit in your bellhousing.
