Ive had my 93 T56 swapped in for over 4 years and beat the ever living **** out of it with my H/C LT1 and its never really given me trouble.it has always popped outa reverse but all the forward gears work well. last year it started getting hard power shifting into 3rd. so before I finish the TC78 build and put some serious power thorugh it (650+) I wanted to get it built. The shop I was going to have do it said to get rid of it and start with something in the 95+ range since the 93's where to weak.

question is how weak are they and why are they weak? I know the 1st gear is different but I thought the shafts were all the same...

 

According to GM, the torque ratings for the various T56's were:

1993 M28 (3.36 1st gear) - 350 lb-ft
1993 M29 (2.97 1st gear) - 400 lb-ft
1994 and up MN6 (2.66 1st gear) - 450 lb-ft

The lower the gear ratios, the more torque (gear ratio X flywheel torque) the shaft had to carry in 1st gear.