You should be able to use carburetor cleaner spray to check the condition of your crankshaft seals, assuming that this is a two-stroke engine. The seals do not wear very quickly and are usually not a problem, but when they fail they'll do odd things to the engine's performance.
My 1984 Trac Clipper wouldn't get halfway up the test hill. My guess is that the difficulty is the crankshaft seals, especially because the hill-stalling problem was accompanied by a slipping clutch. I believe that the clutch plates were slipping from the fuel mixture leaking past the crankshaft seal. As soon as I get the correct seal I'll clean the clutch and report my findings.