What's causing my tcc to lock in and out?

1998 k1500 suburban
I have been experiencing a problem with my tcc kicking in and out in 3 rd and od between 40 and 65 mph. Iit started just doing it in od if under 60 mph. I have replaced the plugs cap and roto,fuel filter. I have cleaned and tested the map and maf sensors,egr valve,ait sensor. I am fairly shure the problem isn't in the trans because I did an intake clean at 2000 rpm with Seafoam intake cleaner and the problem was gone for a day.tcc operated great in both 3rd and overdrive. But the problem came back.
So I did another intake clean with the seafoam and the problem went away for a couple days.but now it's back.

Any ideas/ help would be greatly appreciated.

Test drive watching the misfire counters to see if that is the cause. Also try lifting the brake pedal up with your left foot. That's a fairly common cause of the TCC popping in and out.

Thanks for your reply
I have checked the brake switch.im shure it is not causing the issue. I don't think my scan tool has a misfire counter,or I don't know how to use it. No codes stored or pending. Do you have any idea why after seafoam intake treatment the problem goes away for a day or two?

How were the sparkplugs? Even?, Some fouled?what's the mileage? original spider injection system?

Spark plugs didn't look bad when I changed them. Little to no fouling... they all looked the same. That was the first thing I did. 200000 on the suburban.Fairly shure the original spider injection.

Good to hear on the plugs, can you ride shotgun and watch fuel trim on scanner at the problem rpm? And what did you see to clean the intake?

I have recorded the data while driving...what values should I be looking for ie +/- percent values? I cleaned the intake with Seafoam intake cleaner. It's done by holding the rpm at 2000 and spraying the hole can through the throttle body.approx 7 min. It worked great for a day but didn't last. I tried just holding at 2000 rpm without spraying cleaner to make shure it was the spray that changed the condition,not just long holding of rpm at 2000 for that amount of time. It didn't do anything.after another can of spray ran through the condition went away again.but again only for a short time. This leads me to believe that something between the throttle body and the tail pipe is the culprit.

I was thinking you saw some carbon build up, at pcv, map sensor connection? Are the trim under 15+/- at steady throttle?

The values stayed between -9 and+9. I have also replaced the PCv valve.

Argh, check out this info, 4L60E_80E_CODE_BOOK.pdf

I couldn't find the information that you suggested. I pretty shure it's something telling the computer that it's under too much load like its getting ready to downshift. Could a failing catalytic converter be the culprit? I am going to do another seafoam treatment and record the data during and after the treatment to see what changes. Any other ideas would be appreciated. Thanks

I just googled it, no problem, here's another try, ATSG Comprehensive obd2 Diagnostic Guide For 4L60E

So... I did a fuel pressure leak down test... Failed. Replaced the spider injection and new distributor while it was handy. Runs and performs great other than the persisting tcc issue. Arrrggggg. As long as I keep it under substantial load ,ie, lugging or moderate to heavy acceleration it locks up great.but light acceleration and cruising it kicks in and out.any ideas??