IMO the automatic transmission is working against you more than the engine power. At least with a stick the driver can keep it in gear instead of downshifting constantly the way these trucks like to.
On my automatic trucks of that vintage I like to pull the part throttle kickdown valve body add on thingy off and throw it in the trash and put a block off plate on the VB. It only changes 1-2 and 2-3 shifts but it helps reduce the number of shifts at lower speeds. If you don't throw it in the trash you can use it on older cars with big cams to help keep them in their usefull power band.
Another thing I like to do is block the OD acumulator in the VB, the spring is usually broken anyhow, just pull the piston (no VB removal needed) throw away the spring and fashion a blocker from a wooden dowl to keep the piston from moving at all when the cover plate is added back.
