93 Dodge Dakota surges at consant speed? Help.

I can't figure what the problem seems to be, the trick has been acting this way for about six months. The truck seems to run better when it's cold but
when it gets into the hot lean burn cycle it surges when I'm traveling at a constant speed, and no I have not checked the error codes. The truck also has an iregular idle, and is hard on gas but that could just be my driveing. I also noticed the last time that I changed the oil it smelt like there was a srong mixture of gas in it. so far Ihave repalced the MAP, TPS and the idle controler, but none of these have helped. Truck has over 310000 Km on it.
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