[grinch4om]

do you have a cat converter on it? sounds like one is plugged up, gets worse as it warms and eventually cloggs completely. try unhooking it and drive. if you by chance have the original pellet type, take it off and replace it with a high flow one. On another note, hook up a fuel gauge, drive it and glace at it when it hesitates. You may have a delivery problem. It does not sound electrical to me also make sure the rockers aren't too tight, lifters could be pumping up at higher rpms and hanging open the valves