Pontiac Repair: performance of 1990 pontiac bonneville, fuel mileage, pontiac bonneville

Question
my 1990 pontiac bonneville actually has two problems. first is that my 3800 engine is getting rough gas mileage , about 17 mpg on highway and seems like it doesnt have the spunk it should have.Second when i drive the car in overdrive and the rpms are around 1800-2000 the engine starts jerking ,like its trying to stall.but if i drive the car in drive, this doesnt happen. the car has 150,00 miles on it and i have already replaced the plugs ...its driving me bonkers

Answer
Anthony

Check your ignition wires,usually they will short under load and when the transmission goes into 4th gear lockup,also this will cause a drop in fuel mileage if it does infact have a missfire,also check your fuel filter and replace that,its inexpensive and can give you better performance.

ED