At a minimum, make sure you lock the TC clutch when in 4th. The the TH700R4 bypasses the trans cooler and dumps the fluid in the pan when in OD (4th). Prolonged 4th gear use can cook both trans and fluid.
If you examine GM's scheme for fourth gear TC lockup, they prefer to drop into 3rd and unlock the convertor when more load is encountered in OD situations.
Cheers,
MV
