[old_tv_nut]

I'd also bet it's IF alignment

A couple items that are probably not a fix, but I would try really simple really quick things first:

I assume the cable from the tuner to the IF is good (center conductor and ground)?
Replace/swap IF tubes just in case one is causing trouble.
It only takes 5 minutes to rule these out. Although they aren't likely, if they are a problem, chasing alignment will be futile.

Next check resistors and other parts.

Then consider doing alignment