I've been trying to figure out this hard shifting problem on my truck. when you first start driving the shift are too soft, and there is a little slip on from 1-2 at wot. It shifts like that for the first shift, then it gets progressively firmer as you drive, to the point where it catapults the whole truck or barks the tires, thats cool at wot, but not so much at light throttle. I've gotten use to letting of the gas at the 1-2 shift.

I have the 1-2 upshift modifier table set to -20 at low fluid temps and -40 at high temp up to 280 ft/lbs. This helped a little but still shifted way too hard at light throttle.

Here is my theory on the situation. I think the looseness of the TB stall at light throttle makes the PCM think that the shift time is too long, the rpms don't drop hardly at all, and the 1-2 time times are always 1.5+ secs, and it will set shift time errors of like 5.5 secs+.

So I set the desired shift time to 10 secs, now it shifts a lot better, still firm but not too hard. But when the trans is cold it shifts way too soft. I'm going to reset the 1-2 modifier to 0 psi at low temps and see if that helps.

It only seems to be the 1-2 shift that does it badly, the 2-3 still gets firmer but its not as noticeable.

Could there be another line pressure table in the PCM that we can't adjust. Or could it just be, that the pro series band grips better, the hotter the fluid gets?

Man I wish I would have gone with vac mod line pressure.

The trans has this in it.
-Pro series band
-transgo shift kit
-vette servo
-stock accumulator setting
-Z-pak 3-4
- plus all the other goodies unrelated to shift firmness.