I just recently bought G20, looking to restore. Ran amazing for it's age, until I filled gas tank then it started hesitating, lost all power going up slight incline. Changed fuel filter as soon as I got home. Ran perfect again for about a week, now it's back to hesitating and losing power uphill. I did refill tank. Could be dirty tank continuing to clog fuel filter, intake manifold gasket? Any suggestions on how to test would be greatly appreciated. I don't want to throw a lot of unnecessary new parts at it.