Changed trans fluid in my TH400 and now it wants to slip and not get into gear.

[HeavyHauler]

Well I got the trans pan sealed tight with zero leaks. I started the truck and put in 5 quarts while it was in neutral. I let the truck warm up and made sure the dipstick was reading at the full mark.

Truck still doesnt move. I shifted through all of the gears and nothing. The trans is original to the truck and has ALOT of miles on it. i cant think of anything else to check. I guess it need to be rebuilt.

Instead of rebuilding it though I might just get a rebuilt 4L80E instead and just put the TH400 in storage.

I am bummed out though as I was hoping to cruise it around some more this summer.