last night i was on and someone had a almost identical issue.ok this is the deal,i blew my tranny input and output shafts so im waiting too get them in my built tranny thats on the bench.so i have a rebuilt stock tranny in my truck for now.every since i put it in it has shifted in 3-4 slowly ,it would almost rev between 3-4 .anyway just the last 2 days for no apparent reason its been like slipping in 4th if i give it gas it wants too creep up so i let it immediately back off and just cruise and it seems to be fine.temp is staying at 110 so its not getting hot .ive been through 6 tranies so ive been real gentle on this 1 not too ruin it.seriously ,i havent even been hammerring it at all .if i put it in 3 it does not slip at all 123,no issues.leave it in 3 no issues.just randomely does that rev when i accellerate at cruising speed.yes ive checked the fluids.i reeeally dont think theres any reason to be slipping.last night i read a similar thread ,that i think james burtok answered ,and explained that it could be something in tune,or about tcc if i recall.could i get a little refresher or opinions.i always wanted my 3-4 line pressure raised .so if u guys think its in the tune can i post my tune and someone fix it poss,or at least raise my line pressure or make ness adjudstments,i have hp tuners and unlocked tune.i just dont want this too SLIP through to be a big problem right now waiting on my tuner too get it back too mee ,sometimes it takes awile through him cause hes extremely busy of course.i dont feel like doing a nother tranny change right now so i want too kick it in the ***.thanks ahead guys.well appreciated.

 

no one ?nothing?

 

4l80e should fix it.

 

for what its worth some times my 1-2 will slip real bad.. other than a rebuild and build the **** out of it I got nothing..

 

I'm no math wizard, but a 6.0L engine and 15psi and 6 killed 4L60-E's = time for a 4L80-E. Do you really want to have to think about busting the transmission every time you want to hit the gas?

As for the 3-4 problem, do you have anything you can use to log line pressure while slipping is taking place? I just keep thinking to myself SIX TRANSMISSIONS and have to think there must be somthing wrong in common with all of them, the program? At 15 psi on a 6L it stands to reason that you should be breaking hard parts, not having slippage on a fresh stock build.
I wouldn't normally suggest one because it's a "band-aid" to bad tuning in my opinion, but you might consider vacuum modulation for line pressure at this point. ...that is if you intend on sticking with a 4L60-E.
25 minutes? lol
patience grasshopper

 

i really do understand abou the whole 15 psi ,but i really have been taking it reeal easy .and i dropped too 9 psi .there is no reason for this too b e slipping already ive been taking it like a baby till i get the har d parts in my other 1 .i know allen only raised line pressure 15 percent on my tune for the broken 1 and thats the same tune in it now.i just think that this tranny needs alittle more tunage .it has been been a reel weak 4th all the time its been in .about 1000 miles thats it .it has always had that rev between 3-4 .and if i hold it manually in 3 it stays there fine even at wot no slippage.and 4 doesnt do it all the time .it just randomely slips when i lightly accaalarate . i just didnt want too wait a week till it was too late too do ant thing with the tune.i thought maybe someone could play with it for me.and sorry about impatience last night ,i was going to bed early i spent the weekend in the hospital and just wanted to see if i could get a quick response.let me know if theres anything you can do or tell me.thanks

 

You have a high-stall torque converter. Are you sure that what you feel isn't just pulse width modulation on the lockup clutch catching up with the load? This could feel like slipping when it happens. There will be RPM rise if the TCC is being modulated.
Every 4L60-E I've worked on gets PWM removed in the valvebody by preventing movement of the pulse valve with a stiff spring. You could do the same.

 

if it is tcc you can adjust the minimum pwm to 80 or 90 percent

 

if i sent you a copy of my tune could any one here try to do this for me?it weird i can go out drie it itll be fine then go for another drive and itll do it .then fine i can go full throttle .its def something funky.bye the way bertok im sorry for not updating my sig but i pulled the torqe and tranny when it broke .wile im waiting to fix it .i def think it tunage issue.