Exactly. Torque converter drainback is a very common problem with torqueflite's when they sit over night. What's happening is you put it in reverse and it doesn't move then by the time you get it in drive the torque converter has filled enough to propel the vehicle. Next time you start it do what Jimmy said and run it in neutral for 30 seconds or so then pop it in reverse (or drive) and I bet it'll pull fine.
