Bad Finals or Backswing?

I have a Uniden PC78 LTW that I bought used and have used daily for over 3 years. As far as I know it's stock and it's a good loud talker. I have it in a dump truck hooked up to a Wilson 2000 antenna with 1.3 SWR's. Twice in the last week, after it's been on for about 8 hours the needle will drop or waiver instead of jump over when transmitting. The red transmit light comes on but no output, no antenna light.
If I shut it off for 5 minutes, it will be fine the rest of the day, loud and clear. The case doesn't feel hot at any point. Are the finals going or is this "backswing". Is this radio repairable from a mechanical or financial point of view. I have 2 other radios, but this would be my primary backup if salvageable. I'm going to pull it out and check all the connections and solder joints as a start. After that it'll have to be sent out if it's worth it.