its a bit odd to tune by MPH but you'll get the hang of it if you do a bit of tuning, then log and graph MPH, RPM, and selected gear. you will see exactly where you need to change the MPH points to achieve your RPM target

i never practiced much tuning the LT1 ecm because all mine were manual transmissions

everyone is different but lately i set a goal with automatic transmission tuning where below 25% throttle it shifts through the gears gently and generally wont downshift. then above 25% throttle i want the thing to be in its powerband all the time either by kickdown or shifting. due to gearing that's not always possible but i get it as close as i can.

speaking of keeping in the powerband, i drove a porsche with a tuned CVT recently that thing had not a lot of horsepower, tiny engine, but had a huge power spike at like 6500-7000rpm. when you floored it the CVT slipped up to almost 7000rpm and held it there right at the rev limiter by changing the ratio. so even though it had a tiny engine, the transmission made it have maximum horsepower from zero to infinity. that should be the goal with transmission tuning. maximum possible time in peak power.