Done with 700R4

[Cuba]

I got the truck back today and the transmission shifts 1-3 fine and at 45 mph I have to let of the throttle and it shifts into od. Is that the lockup converter or something else is up?

I wonder if you have a tach... if you do, what does tach say @45mph when you're just accelerating to 55, let's say?

You say you need to let off before it shifts, but it could also be normal to hold 3rd, depending on rpm and load. I may not shift into 4th until I hit 50mph or 55mph and that's me trying to get to spred on highway, not passing, but getting on.

 

[Cuba]

Lower gears...
Think of overdrive like 4th gear. You really don't want to lug your engine on the highway, and 700s hate to get lugged. If it's hunting back and forth from 3rd to overdrive, it will create nuclear fission and MELT down.

I partially agree with this, if it's hunting gears, they hate it. Just trying to see what exactly driver is doing vs trans 1st.