so i have a 350 with impco propane system and its been acting up these days. it runs perfect except when i go up hills(on highway). if i start goin up a at say 2200 rpm, and i keep it there, there are no problems. but if i start at 2200 rpm and i advance the throttle, the engine just goes to ****. missfires and feels like its gonna blow up. all i have to do is take my foot off the gas and go again and it will be fine unless i accelerate too fast. would this be a vacum leak on my timing advance or something??