Added the weight of ONE person, jerking is back!
 

I earlier had some problem with my blazer jerking at steady speed around 45mph/1500rpm. I can't tell you what I did to make it go away, as I kept trowing parts at it all last summer.

Usually there is only me, my wife and the dog, today my father also was with us and the jerking was back. Dropped my father off and drove home, the jerking was gone.

Why would the adding of one persons weight make the jerking come back?

sounds like something is wrong with your suspension. did you replace the shocks? is your rear end sagging?

I feels more like a transmission or engine problem. New shocks and no sagging :)
Thought it was my lock up solenoid, but that should not go away with less weight.

how many miles do you have on your blazer? is it the original transmission?

118060 miles with original transmission :)

sounds like the engine is skipping

Thats something I never heard of before. Could you explain?
If it only would pop a code, but there is no codes.

have you done a tune up recently?
replaced the injector unit?

I have changed just about everything, plugs, wires, coil, air, fuel and oil filter.
But not the CPI unit.

Do the RPMs fluctuate during the jerking? If you give it gas while it's jerking, does it seem to respond well?