When I'm driving the engine starts jerking like mad when it hits fourth gear and is "cruising". The rpms seem like they are really low, so can I adjust this and how, or is there some other known problem with this? Thanks, I need to get it fixed to go on a road trip soon, so quick help would be greatly appreciated!!

Thanks

By car I meant van and it's a 1944 Pontiac Trans Sport

Ha, and by 1944 I meant 1994. Okay, no more typos.

When was the last time you did plugs and wires? And if you did them what plugs and wires did you use?

I'm switching them out right now, actually. But, it doesn't seem to be that. Wouldn't it jerk at any gear if that was the case?

...The rpms seem like they are really low, so can I adjust this and how, ...
...this "car" gear ratio makes the engine rev really slow....like 1650rpm at 60mph....but there is nothing you can do about that...except run in 3rd gear...
..can you describe "jerking" ? is that like missing spark? is that a mechanical vibration?...

With a slight miss due to plus and wires it can Jerk under load... Say the load of pulling a hill in Overdrive With TCC Lock at 1650 Rpms... This will cause the engine to stumble or jerk..

But this can be anything from a Fuel injector, to a plug, to a plug wire or even a coil thats getting weak..

Have you changed the lugs and wires already and have they made a difference? If you changed them out what did you have in there before?

And the Jerking you described, Did it feel like a Bad intermittent stumble, or a constant Miss?

"except run in 3rd gear...
..can you describe "jerking" ? is that like missing spark? is that a mechanical vibration?..."

it's like if a giant is shaking the van front and back. It could give you whiplash if you had a weak neck.

I vote plug wires.