904 upshifting

Howdy I have a 904 with a shorty kit, Transact Manual trans brake valve body, 5000 Turbo Action converter in a SBM powered FED. It's a three and a half hour drive to a track for testing. Trans shifts up OK on jacks, but on a quite country back road I couldn't feel it shift. There are serious limitations with that type of test track. Why when I shift with the vehicle on the ground can't I feel it? Is it because I need to be well over the converter stall speed? I've been a clutch guy in the past and I'm not familiar with converter equipped cars.
Cheers