The 91-93s have a 4L60/700R4. LT1 cars have the 4L60e. The 91-93 cars have a manual shift cable, and the 94-96s have the computer do the shifting. The tail shaft housing can be different on different years of the 94-96s. The 91-93s are all the same.
The 91-93 cars have a gear driven VSS as well. If you are changing tire sizes, you should re gear the VSS. There are two types of VSSs, one for the 34-39 tooth driven gears, and one for the 40+ tooth driven gears. You can also get 15, 17, and 18 tooth drive gears. The driven gears are difficult to find, and do not have a shaft on them. The pinion gears are a little easier to get. There is a chart, and formula on the Speedometer World site to determine what gears to use with what gear ratio, and tire size. The 94-96s have a tone ring and pickup, so are not adjustable. They use the computer to modify the signal for the tire size, and gear ratio.
The gears are marked for # of teeth both with an embossed number, and by the color of the gear. The FSM also has some of the possible ratios and tire size combinations in the transmission section.