1989 Isuzu Pickup XS(2.3 L-5 speed)--just bought the truck about a month ago from a certified mechanic who did a lot of work on it to update it. apparently after he completed the work he let it just sit for a while(?how long) which may explain some of the problems i am having. around town it runs smooth as silk. at speeds above 40 mph there is a hiccup or **** as though it is misfiring. it doesn't happen continuously but seemingly when it wants to. it has done this since i have had the truck. i have driven it no more than 1000 miles. at first it was only happening at speeds of 50 or above but now at 40. it is not the plugs. took out the plugs and they looked almost new with no carbon,just a little white deposit. i replaced them anyway but no change. what do you think? very annoying. also,on a cold start in the morning i tap the gas a couple of times and then crank the engine but i have to tap the gas a couple of more times to keep it running. it does the same thing if i leave it for,say,4 or more hours. the carburetor looks extremely clean and the air filter is brand new. vacuum lines have been replaced as well as the oxygen sensor. also,annoying. ideas? and the engine seems to be burning rich as there are some very strong fumes coming out of the exhaust. and the temperature needle only budges about 1/10th of the way through the range. it is not running hot as i have hot heat and the antifreeze level is fine. i guess i need a new thermostat? could the thermostat be the source of the fumes. can you help me? are any of these problems related? great little truck. runs like a top around town but simply has a few problems i hope have relatively simple solutions. any assistance you can offer will be greatly appreciated. thanks,robert