If the amps are running cool during the time "the set will run fine for
a couple of hours", I'd check the convergence generator area for a bad
connection. Since this TV uses standard STKs, any schematic you may
have that uses the same amps will show the pin outs of the STKs. I'd
run the TV without the amps, and scope the input signals when it's been
running a while. I'd also carefully check the +/- supplies, as loss of
one can cause the STKs to run hot and fail.

John