I've seen this on an 02' it would go down the freeway at 70 but it took forever to get there and would only maintain 4-5K and any throttle it would drop off. new pump a year ago and it was all good ever since. Worst part was the guy had it to two other shops before. one put a new set of injectors in it and that didn't work and the second did a s366 turbo swap and sent it out he door.
Some people and some shops I swar It's not running correctly I know lets throw a mod at it:roflmao:
Glad you got it worked out Adam...