Diagnosis help

[98Bacon]

So myself and a buddy put a new GM L31 crate engine and a rebuilt transmission into my 98 Silverado. The motor has good power and transmission functions well. Timing is set properly and is reading - .02 between 1000-1200 rpm. However, at highway speeds the truck seems to kind of quickly buck or shutter after shifting into overdrive, feels like another upshift. It isn't totally consistent, however it is frequent. I'm scratching my head trying to figure out exactly what could be causing this, I guess it could be a lot of things. I'd appreciate any ideas about what this could be or ways to diagnose it.

Here's a list of new stuff that went along with the motor and trans:

HT383/RAMJET CAM
COIL, PLUGS, WIRES, DISTRIBUTOR
MAGNAFLOW CATS, O2 SENSORS
RADIATOR, TRANS COOLER LINES
EGR DELETE
BLACKBEAR TUNE
- 89 octane
- zero torque management reduction
- stock shift firmness
- egr delete
VARIOUS SENSORS

Thanks for reading, appreciate the help.

 

[jeff1953]

have you checked the torque convertor

 

[98Bacon]

No, how I would I go about diagnosing a torque converter issue?