Sorry Big Jim missed your reply.Motor has been rebuilt by a shop.Has a brand new tune up,does not happen on highway,does not do it anywhere except up steep long grades in the mountains,200 to 300 hundred yards.You can punch it on level ground and it runs like a bat out of H**l.Here is exactly what is does,runs great until you get over half way up a steep grade,then the motor starts to slow down until it stalls.You go to start it back up,a few more cranks than normal,and then you see all kind of black and you have to run the engine about half open to get it to smooth out.The vacuum advance is working the choke is working and fuel is not contaminated.Again sorry about not seeing your last reply,thanks.