Will shift kit help?

I have a 2001 Montana with 245k. I seem to have all the classic problems with 4t65e trans...no 4th gear, long delayed shifts, hard shifting & whining. All present when I got it at 229k for next to nothing. I know what the causes are for the most part. My question relates to the delayed shifts. It not only shifts long & slow, but shifts seem to be at way too high of RPM, like it's looking for a pressure value that can't be achieved at proper RPM so it waits and goes higher. ??? Also when accelerating, the RPMs are higher than they should be to engage torque converter and transfer power. I suspect internal seal leaks and therefore lower supply pressure. I used to have a Venture with the 4t60e trans, that one had amazing power transfer and could smoke the wheels easy and was very fast even with 200k miles. The Montana is a dog in comparison. Even tho it's got higher miles I think it could do a lot better! Would a shift kit (spacers & springs only) help with line pressure to torque converter and thus more positive power transfer / lower RPMs? Or would it only affect shift firmness? I'm also considering a new 4th hub to restore OD. Is it worth trying either of these?

I know a rebuild/replace is in order but I don't have the time or money, along with the other problems the vehicle has. Just want to improve performance and extend its life. Thanks for any help.

Shift kit won't help in your situation. Your trans clutches are likely going and will be gone soon. Draining your fluid to install a shift kit would probably kill your trans anyway as the fluid is probably full of clutch material is probably the only thing keeping it going at this point.

I've already been down this road. Started with all the symptoms you mentioned much earlier on. I did put a shift kit in it which let it run another 50,000 Kms before it was obvious that it was slipping in 4th and not going to get better.

I had the trans rebuilt, the shop packed the clutch packs with additional disks to reduce the movement of the piston(s) and firm up the shifts. They build HiPo trans for racing and this is a common fix for most GM transmissions. In addition they replaced the accumulator(s) and removed the shift kit.

Van has run strong since repair at 228,000 Kms (got 280,000 Kms now) and has this distinctive solid shift between 1-2, 2-3 and 3-4 with a hint of OD at highway speeds.

If it is a 'dog' now, it would be my opinion that the trans is slipping badly. Our EWB van is a hauler for the kids still in university and it has been our hauler for over 10 years now. If our daughter ever finishes school, we can finally retire it!

It gets 33 mpg (Imperial gallon) and runs like a top.

My advise would be to either kick or play; - Get it fixed at a reputable shop or deal it.

Are you saying that the higher rpm at acceleration and prior to shifting is a result of slipping? It doesn't feel like it's slipping when accelerating. It's still pretty smooth. I just want to know if a shift kit improves input pressure to torque converter, thereby giving a more positive transfer of power (hence lower RPMs to make vehicle move).