4L80E Trouble (maybe?)

I took the kids camping this weekend and had a problem that fixed itself, so I'm a little worried that I might have something expensive in my future.  It's a 1993 Chevy P30 chassis with the 454 and a 4L80E and the chassis and trans have 110k on them.  On the way to the park, it ran great on the interstate with smooth shifts both up and down.  When I got off the interstate, though, it suddenly started hanging up in first gear, acting like it didn't want to make the 1-2 shift.  If I let it rev up fairly high - no tach, but going about 10mph faster in 1st than normal - and then backed off the throttle, it would shift fairly roughly into 2nd and then would shift smoothly into 3rd and then 4th.  Going up a really steep hill it seemed to really hunt between 1st and 2nd slamming back and forth between the gears.  After sitting for a day and a half at the campground, it ran completely normally for the drive home.  Shifts were smooth and at their normal intervals.  It is due for a fluid change and I intend to do that before my next trip but the current fluid level is good and nothing smells or looks bad about it.  Do I need to be hunting for a new transmission?

Did you have any luck figuring it out?  Sounds a bit like shift flare to me, but that’s more of an issue on the 4L60.  

My 4l60 did the first gear thing, had to get the rpms high then let off and it would slam into second. It was a broken sun shell, those were the only symptoms though.

No experience with an 80

Nope, I got nothing on this.  Before we go up to Gen Con in a couple weeks, I'm planning to dump and replace the fluid and see if the problem comes back. 

It didn't really seem like a slipping clutch, though.  There was no lack of forward momentum at all - it was just like I had pulled the lever down to "1" and tried driving around that way.  The shift was a bit rough when it finally came, but it just acted like the TCM wasn't commanding the 1-2 shift for some reason.

Most likely the piston valve in the valve body are gunked up or galled.  Pretty common issue.  They stick until you let off the throttle, the pressure solenoid increases pressure, and wham... it breaks free and hits second hard.

The pressures seen by the valves are controlled by a main pressure solenoid.  It's possible the PCM was activating the 2nd gear solenoid and sending pressure to the valve, but the valve was stuck and didn't want to move.  The main line pressures are highest at idle and WOT.  In the middle throttle, they keep it a little lighter for smooth shifts.  WOT defaults to max pressure, and low throttle/idle shifts can save the clutches a little with higher pressures/faster shifts when there isn't much load that you would complain about hard shifts.  My guess is the PCM activated 2nd properly, the valve stuck because you were at mid throttle, then when you let up the pressures increased and actually got the piston to move... quickly.

Doesn't sound like a flare to me.  It's staying engaged in first and hitting second hard.  A flare would "neutralize" for a second, but he's not describing slippage, he's describing late shifts.

If it is the valve body, the fix is either clean out the gunk, or if its galled there is a bore/sleeve kit that fixes it up.  Of course, a reman 4L80E valve body isn't that much these days.