Help me understand this transmission problem
 

My 2000 Tundra had a issue year or so back where the coolant mixed with the tranny fluid. Anyway I had it flushed several times and it began working normal again. In the interim I bought a rebuilt unit to swap in (I got it dirt cheap) when it eventually failed from the abuse.

Well the other day it started slipping badly at takeoff from a stop. The weird thing is I can manually shift from 1st to second to drive and it operates seemingly fine but in Drive it slips(from a stop or moving slowly). Does this indicate a valve body issue? Why would first operate correctly when the stalk is in first but slip badly when in auto (in first)?

As a side not the tranny I picked up cheap turned out to be a 2WD tranny so I'm searching for a replacement and/or deciding if this one can be fixed easily enough.

lendaddy,

Most automatics change the fluid pressure when shifted manually. By dropping it into low, you are applying more pressure to the low/reverse clutch packs. Nothing wrong with your valve body. You soaked the clutch plates with coolant when you had the leak. Once they start to slip, it's downhill fast.

Rex - or know locally as Tranny Source Rex

Great info, thanks. At least it makes sense to me now.

When you had the coolant and the tranny fluid mixing you replaced the radiator right?

Yes.