i have an 88 chev 3500 with 350..originally the trans was a th400, but it sucked on the highway...i converted it to a 700r4 with the proper driveshaft and pcm and it was way better, but it always had a 2-3 flair meaning that the shift between 2 and 3 took longer than it should, and rpm slightly increased...this conserned me, so i put in a b&m shift kit in it...when i took apart the accumulator housing, the springs were broken on both sides...i figured"a-haaaa"...not so...the shift kit made it better but didnt cure the problem...(the shift kit replaces the springs with spacers)i also installed a new seperator plate at the time of the shift kit, because the check balls wore the plate out...just recently, i blew the pump in the trans, and pulled it out for an off the shelf piece i had kicking around...this one shifts perfect...i plan to repair the other trans, as it looks to have been recently rebuilt, but i want to fix the flair at the same time...i checked the pressures when i first installed the trans, before the shift kit, and the local tranny guy said the numbers looked fine, although i dont remember what they were...could it be worn out servos leaking at the shaft, or seal...any info would be great...

I can relate to a THM400 in an 88 Dually with a 454, I'm in the same 'boat.' I would think if the pressure applied is the correct amount, and the amount of time oil pressure is shown, then maybe the piston for 3rd may be leaking, too much clutch clearance, to burnt discs.

I'm talking about the time from when 3rd is selected to the amount of time 3rd is actually applied, as compared to 1-2 shift. If time for 3rd pressure is selected is slow, time the indication on the gauge, then it may be a slow valve.

As said, compare the times of 1-2 shift to 2-3 shift, time the pressure is indicated to time the next gear is applied. Make sense?

Your throttle valve (TV) cable may be out of adjustment or the TV spring may be short. Here is a good article on the subject:

TV Made EZ Part 1 (http://www.tvmadeez.com/article/index.php)
TV Made EZ Part 2 (http://www.tvmadeez.com/article/part2.php)
TV Made EZ Part 3 (http://www.tvmadeez.com/article/part3.php)

did the tv thing a million times, but thanks...also, the 1-2 shift is now very positive since installing the shift kit...i was thinking possibly bad clutches, but it doesnt slip,it just flairs...once in gear, its solid...i cant do any pressure tests anymore cause the trany`s outta the truck with a bad pump...in addition, i`m a little lazy on tearing into it as i fix everyone elses crap all day long...lol...