What does a bad torque converter feel like, symptoms??

You're not getting it; Saying something is good doesn't necessarily mean it is so.
>If you have been driving the car with the KHers and have not experienced any binding brakes, ok then they must be good. I get that. Otherwise testing may be required.
> If you have been driving the 98 for several miles with no power issues then it must be good, I get that. But if this is a maiden voyage, then testing may be required.
>With no oil pressure tests on the tranny prior to pulling it down, you are at your own mercy, in having a look-see. I fear if the new TC does not solve your problem, you will need to take it down yet again. The pressure test is the only way to prove the tranny is any good, and if you don't have a test bench, then the tranny has to be engine driven,ie;reinstalled.
>I get that there were vibration issues,but others have addressed that.

> so just what cam went into the 98? Was it degreed in? You got any unusual noises? Were there other changes at the same time? Like ignition timing? or a 4bbl set-up?
>Is that old 904 a stocker? Was the KD mechanism hooked up and correctly adjusted? Was the cooler line flushed prior to being hooked up?Did you preform an air-test on it before the VB went on? Since it is now on the floor, this would be a good time to remove the rear extension and verify that the governor is correctly installed. Or did you install a shift kit with a governor bypass?
> what rearend is in it; an 8.75 with tapered bearings?You probably know that if the bearings on these are loose, then the drum can be caused to rub on the shoes. Or something with ball bearing axle-bearings?
>How about the exhaust? Is it known to be free-flowing?

Jake
I know you are a smart man, I have seen a lot of your posts.But sometimes we tend to move a little too fast, and might miss some little thing.
So, honestly. I'm not trying to be a dick.Sometimes it just happens all by itself,no trying involved.
Hopefully it really is as simple as a failed sprag ,in the TC.