05 duramax problem

[scotts62]

There is a guy that I work with that has a problem with his 05 duramax 6.6 automatic with about 80k. I haven't had a chance to check it out yet until be brings it to the shop next week, he lives a bit out of town.

He was coming to work driving about 40mph and said it just acted like there wasn't any power there all of a sudden and the rpm won't go past about 2200 and is real erratic as it does rev. Said it starts up and idles fine and can drive it up to about 30-35 mph before it starts cutting out and running bad. He got it home and changed fuel filter just to see but it didn't help. After it sat for a bit he started and said it reved up like normal then a few minutes later went right back to running bad. Just wanted to get the ball rolling of things to check or if anyone has run into this before by chance?
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