This section is for automatic transmissions. There are a lot of ways to modify a transmission. Always try to end up with a package well suited to the engines output. If, for example, you have a 308 producing 350 to 400 Hp, you will obviously need a good torque converter, one that will stall to just below the start of the torque curve of the camshaft.
There are many internal parts that can be improved in Trimatic transmissions and TH700' S. The first thing will be a shift improvement kit. This will alter the amount of hydraulic pressure applied to the components affecting shift. There are many shift kits available, made by many different companies. Too harsh a shift into one gear, and to soft a shift into the next gear is not a good thing. Parts like extra friction plates, High-energy bands, heavy-duty clutches, stronger servo pistons etc, and modification of specific internals will improve the power handling capacity of a transmission.
Another good modification for high Hp engines is to make a transmission Full Manual. In other words, the gear you select is the gear you take off in. The transmission will have no kick down, and will not change up through the gears by it self. This allows a higher line pressure to be applied through each gear and provides stronger shift quality!
If an automatic transmission is built properly, weather it be a Trimatic or a turbo-hydro, it will be able to withstand a lot more horsepower than it was originally designed for. As a bonus, if driven with some respect, it will also last a very long time.
Many Trimatic V8 Commodores have a habit of poor shift control. For example, when accelerating from idle up through the gears, many either miss 2nd gear and go straight to third, or stay in 2nd for such a short time, it's hardly effective. This can be fixed by a reputable transmission mechanic!