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Had to make a family emerg. trip to Calif. and on the way back home thru Colorado, truck went into "LIMP" mode. Stopped at Stevinson's Chev. in Lakewood to have truck checked. The Tech. went thru all the checks ( flow rate, Nox sensor(s) gaskets/wiring) all checked within spec.(spent 2.5 days) Left there and drove another 300+ miles, went into limp mode again, Stopped in Ogallala, Neb. at Schmidts Chev. and went thru a battery of tests and re-gens with no faults found, all "codes" cleared and back on the road for 150+ miles with no issues. Got back on the road the next day and drove 200+ miles and the DIC read 29% DEF remaining, so got the freshest 2.5gal jug of Blue DEF (under 45 days old) I could find and pored it in. Drove another 300+miles, and up pops prompt "DEF quality poor, will lower vehicle speed to 65MPH in 76 miles". It appears that when this prompt comes up, it appears at the same point in the limp mode sequence(reads the same mileage and never counts down and always at the 65mph portion of the limp mode also). This prompt stays up for about 10-20 miles and then, clears and the truck will accelerate and I can set the cruise and go back to normal driving. So, any GM techs. out there with a suggestion/fix?? All Gm checks have been done and we had this issue once in the first 5000 miles of ownership. I'm figuring it is something that is hard set in the ECM memory or whatever it is that sends a message from the DEF sys. to the ECM. All I know is that, I really like my truck, but I can't be having this happen every time I take it on a long trip, I get anxiety over this stupid crap (wife included). Chevrolet has got to step up to the plate on this one, they need to replace something in the system, because this is getting very taxing. Chev. needs to delete the LIMP mode speed parameters because this puts people in dangerous situations while traveling the nations Interstates, where there is not a dealer in every small town, We just got lucky. I want to thank both dealerships with the help and getting us back out on the road as soon as possible. MAC