5.8 ltr 351 auto with e4od ( 3 spd + overdrive )
just got rebuilt tranny put in
most everything seems great...

Problem:

Sometimes when 1st starting off truck in drive it doesn't go anywheres.
Push down hard on pedal, stays put, engine revs & doesn't move.
When i put manually in 1st gear it fixes it...
when i put pedal to floor it seems to downshift and then go..
There is no kickdown cable on this tranny, all electric.
I also notice while on hills when i put in reverse it always goes into neutral....parked uphill...

Anyone know what might be causing this?
I first thought torque converter, but now I am wondering what deal.
I did put a new TPS on it....