I have a 01 2500 totally stock, no programmers. Driving down the road, towing my trailerpedal will randomally go into limp mode,2000 rpm only. HP pump? Any ideas?

Is it throwing any codes?
Also, I'll ask now because someone else will if I don't, has the fuel filter been changed recently? If not you could try that as a possible simple solution.

No codes, new fuel filter and air dog 100. Am driving down the road right now with family and it has happened at least 20 times in 4 hours, 8 times in last hour.

Did it do it before this fuel filter?

this has been happening the last few times I have towed before and after the new filter.

MAybe you should check it for codes. Its about got to have something in it.

Just checked for codes and there are none

Would be interesting to see what the fuel supply vacuum is. Maybe a restricted fuel supply line. Could be a kinked hose near the filter housing, could be that the sumb is partially plugged in the tank. Hard to say unless you can measure the vacuum when its actually doing it. Regaurdless of that all the duramax's I've worked on with plugged fuel filters going in and out of limp mode set codes for low fuel rail pressure during power enrichment. If its starving for fuel it should have a code. I worked on a LBZ a while back that was setting a MAP and MAF performance code and kept going into limp mode at random. Ended up being a broken MAP sensor signal wire near the connectors on the driver side valve cover.

I have a air dog 100, I checked the fuel pressure and it was at 9.5psi. I also just installed a new maf sensor.

I have a air dog 100, I checked the fuel pressure and it was at 9.5psi. I also just installed a new maf sensor.
Air dog 100? Must be a lift pump of some sort if you have pressure at the test port, should be vacuum if you don't have a lift pump.

Yes it is a lift pump.

I have a 2001 gmc 2500hd duramax ext cab short bed loaded 160k miles new injectors @125k great truck but i do have the same problem have had it for 5 years, it only happens when towing or when driving 70mph and 2000 rpm steady for a few min. if i go up and down a couple of miles it will not happen sounds crazy but truck runs perfect no codes.Read a post here a while back and it said it was in the original progaming of the 2001 models and the way he solved it was to put a 2002 computer in it. Mine will go into limp mode only @ 70mph i could floor it and hit 90 without a problem.Remember i have had this problem for 70 k miles so check all the obvious first. mike