You can turn the EPC solinoid screw to increase the PSI which will give firmer shifts, never seen it done on a 4r70, just 5r55's.. But as long as the solinoid has the screw on the back it'll work.
Where would that be located if it had one. My trans shop said it was there but didn't get into detail.
ok I'll take a look for it sunday
how much should I turn it? maybe like a 1/4 turn.
oh yeah.....counterclockwise or clockwise.