98 Venture stumbles at hiway speed

I have a 98 venture. For some time now it will stumble or chug when I am going at hiway speed - it usually happens when I start to climb a hill but it hasen't shifted down yet. Once it downshifts it smoothes
out and accelerates fine. It feels like it isn't getting enough gas.
I have had the intake manifold done, the ignition wires changed and the injectors flushed with little improvement. I have seen similar problems identified but have never seen a solution.
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Has the fuel filter ever been changed?
John
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This can be caused by a secondary ign. misfire like a bad plug, but is only evident under load such as in o/d pulling a hill, or the trans lock up clutch in the torque convertor is shuddering/slipping, but this is much less likely.

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Have you checked the computer for codes?

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to stumble (?). They reset the computer anyway but this didn't help. Fuel filter was changed - a little better for a while (few weeks) then back to the same.
Problem happens after about 1/2 hour of driving at hiway speed. It is much more prounced when towing a trailer.
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Hi Guys, I don't have an answer, but I have a 97 Venture with the same exact symptoms. Here is what I have replaced so far:
Engine at 89K miles, Cleaned fuel injectors, Fuel filter, Plugs, Wires, Coil for cylinders 1 & 2, MAP module for coil, Transmission checked 3 different times.
Still bucking up hills. Occasionally I get a code for misfire on cylinder 1, but this is never reproducable when in the shop.
Mine also is only apparent after about 1/2 hour of run time, so it is very difficult to find.
I just picked it up from the shop again today, and I will be driving it from Massachusetts to Delaware.
I'll let you know what I find next.
Good luck with your van, Needless to say I really HATE mine!!

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