HELP Please...Chevy Transmission Professionals 4L80

I have a service van. 2006 Chevy Express 2500...3/4 ton with 350 6.0 gas Tranny is a 4L80 with 147,600 miles. Has the towing package.

Now with all that given here whats happening. Its an intermittent problem. I can drive around town for a while then leave a light/spot sign. Now when it shifts it's feels like i gotta shift kit (through all the gears). Then i park and shut it off for five minutes (give or take a few). Now it shifts fine. Untill it wants to repeats its self.

I had the fluid (Dexron-VI) and filter changed also added sea foam for tranny. drove it 5 miles, problem returned. Still intermittent...

Thanks, Jeff
Anything with 4L from Chevy stinks....4L means get your wallet ready....I had a Z71 one time and the trans. went out in it and cost me a lot of money. Hope its a easy fix for your problem.
The 4L80 has a good track record and nothing last forever, even if maintained properly. The problem may be a tired pressure regulator! The biggest concern w/ auto-matic transmissions if you have too go beyond dropping the pan is that they are labor-intensive and you 'can't just' fix the problem. Finding a good tranny shop that won't hurt you is the first step....Good Luck
Just had the same exact issue happen on my old work van. 2500 with 6.0 and 4l80, 133000 on it.

Would drive fine for a little bit and then start bang shifting and revving higher before shifting. also if it drove it long enough with it shifting hard the check engine light would come on. So if your is lighting up there should be some trans codes stored. this will kinda point them in a direction as well

Good local tranny shop test rode and confirmed input vs output rpms will driving, they were showing the ecm a trans slip and thus when the ecm sees this is increases shift pressure and shift points to try and compensate.

tech said the 4l80 are known for convertor issues causing the slip as well as the shift solenoid and cartridges sticking in there bores of the valve body. A lot of times the trans shops have to buy these aftermarket valve kits that they bore out those valve holes and then install these new valves to resolve the issues. Mine needed a full rebuild. seems going rate for this is anywhere between $1900-2800.

hate to be the bearer of bad news, but good luck with it. Its seems all these 4l80 start going out between 120-180k. we had a fleet of 10 of them and they all seem to give out somewhere in there.
I would look on Craigslist for one. Thats where I found one for my 4L60e. I paid $120 and It lasted for the remainder of the time I had it anyway.I had to sell it and the trans was still fine. I put it in myself with help from a neighbor kid and it wasnt that bad. Use a big breaker bar with a pipe for the bolts on the driveshaft/rear end bolts though...
at least with a van its rear wheel drive a little easier to change then frt wheel.
Course trade or sell is always an option.