Chev van jerks on highway after 70Km

I Have an 83 Chev van that starts jerking on the highway after 70Km.I can hear the RPM increasing and decreasing rapidly as it is jerking.It is also gradually slowing the van down as it is jerking,as if the brake is being gradually applied.

I have
1)changed the distributor cap/rotor/wires/sparkplugs
2)changed the fuel filter / fuel pump
3)changed the tranny fluid and filter

:banghead:

Please help.

Are there any other factors such as rainy weather, engine temp, hills, etc?

no..it will do it down hill or up.

dry and warm weather.

Did the jerking and stalling with high RPM just start following some of the changes you made? Did you get a bad batch of gas (water) or are the ignition wires crossed? It sound like a fuel related issue to me as if you are getting an intermittant supply of gas to the engine.
Fred

Did the jerking and stalling with high RPM just start following some of the changes you made?

No...I made the changes as a result of the initial "jerking"

It sound like a fuel related issue to me as if you are getting an intermittant supply of gas to the engine.

I can hear the engine rpm's go up and down as the van is jerking as well.

Well i'm down to 2 things left.
Replace the Carb / drop fuel tank and clean out

and Transmission trouble?

Thanks for the help by the way I sure appreciate it.Any more suggestions would also be appreciated.