How to tell if I got a bad torque converter?

[Nevada City Sparky]

How can you tell? About to put an engine back in after 2nd rebuild. When I had it together, it would shift in and out pretty hard, but I was assuming that was because the tranny was hunting for gears since I'm running 32s with stock gearing at the moment.

 

[Smittty9785]

i had stock gears with 35's for a while and never had slamming in gear

 

[Nevada City Sparky]

Not exactly slamming, its just that when it downshifts to 3rd, it won't stay there very long (maybe 30 seconds or so) before it upshifts again. Then I have to floor it to get it to downshift again. Wondering if this is normal, or if there's anyway to "test" the TC before I put my engine back in.