Even the dealer mechanics are puzzled

[cingulate]

I have a 98 Grand, 5.2L, V8 with an attitude. It only stall\looses compression at freeway speeds for extended periods of time, say greater than 45 minutes. I can drive it hard all day long in town and it won't replicate the problem. On the freeway, the car will eventually come to a complete stop with all attempts to accelerate having failed. I can turn off the ignition, immediately restart it and achieve 60mph on flat\level ground. Forget about accelerating aggressively or climbing hills. I can even drive it forever on rural roads so long as my speed varies. The only aftermarket part on the car is a K&N air intake. Could this be causing the problem. The car is tuned to factory specs. The mechanics want to put it on a dyno and run up a hell of a diagnostics bill. I have to suspect the air filter (damn, I wish I kept the stock filter). Any insight into this problem would be greatly appreciated as I'm headed for Montana in 1 1/2 weeks to do a little fly fishing. Thanks.

[mrbill3]

How long have you had this Grand? Did it always do this? Did you add the K&N? If you did add the K&N, did it o it before you added it or only after?

[xj31]

It sounds like a fuel pump problem.I would put a fuel pressure gauge on it and drive it until it acts up and see if it is losing pressure.It could be the pump itself or the filter on the inlet of the pump.