Technical Th400 auto problems

I have an automatic th400. It shifts to R but in N and D the wheels roll foreward on jackstands but I can stop them with my foot and they don't speed up with acceleration. On the ground, wont move the truck. It was rebuilt and has zero miles on it but sat for about 4 yrs during truck restoration.
Any ideas?

 

Stupid suggestion so if you shoot the messenger, aim high, but you sure it is full of fluid? If they are 2 quarts low they wont shift when they're cold...3 quarts low they don't shift when they're hot.

 

stuck valves in the valve body...., seals/ o rings not sealing adequately resulting in too low pressure to apply clutch packs, low on fluid ???????? check the last one first.

Ray

 

Converter is full?? Sounds like a "no" to me.

 

Sat a while, and then the lip seals can get hard. Trans at temperature? If not, stick a heat lamp under it for a day, and toss a can of Trans-Medic or similar into it to help soften the seals. That will tell you if it's seals, and is usually only a temporary fix. If that does't do it, it has to come out, and be torn down. This is assuming you have everything else covered, ie vacuum line to modulator, fluid level correct, shifter adjusted, etc. I am Butch/56sedandelivery.

 

Not a stupid question. I am the one asking for help. But yes it is full. 13 qts.