Engine that misses

try substituting the ECM with a known good one to eliminate the ECM as the source of the problem

Check fuel filter, pump relay and fuel pump/fuel pressure, or just change both and rule them out as possible problems.

What is the make, the model and the year and engine type/size.

best advice is dont go 40mph in 5th gear... if you are going up a hill at 40mph in 5th gear i have no doubt that it is jerking, your putting too much stress on the engine. shift up to 4th or 3rd you will be fine. 5th gear is an overdrive gear. 55+mph

you might, but it would help if we knew what make, model and year/engine you have-also, is there a check engine light?

• does the engine miss? bumps is a rythmic pattern?
• an engine miss will appear to diminish at higher rpm due to centrifical force.
• other possible problem broken or flat motor mount.
• is the idle rough in reverse?
• if not
• open hood
• start engine
• Left foot on brake (hard)
• start engine
• watch engine as you select drive
• still holding brake with left foot / throttle gas with right foot
• does engine dramatically move?
• if so replace motor mount on offending side
• if not possible engine miss or transmission problems

If you have isolated to one cylinder, you need to look at the compression on that cylinder, should be at lease 110psi. Also check the valve springs, a broken spring will allow engine to run smooth unloaded and miss under load. Remove valve cover and push down on valves, if they move at all the spring is bad. You can also do a cylinder leakdown test and it will tell you if you have a valve or rings going bad.

coil packs or leads probably, does it get worse is you put your foot down?

A RESTRICTED FUEL FILTER WILL PROHIBIT PROPER FUEL DELIVERY....CHECK THE FUEL FILTER OR POSSIBLE A WEAK FUEL PUMP...THE ENGINE MAY BE STARVING FOR FUEL AT HIGHER FUEL DEMANDS

Try Upper engine cleaner from Surabu first..............if that doen't sort it try cleaning the IACV (idle air control valve) with carby cleaner and/or meths