I have a 2008 2500 HD 4X4 4Dr I purchased a year ago in Colorado to pull a 30’ 5th wheel. Not knowing much about diesels, I was not aware that it has lots of modifications, (upgrades, I hope). It runs & pulls as awesome as I hoped except when it suddenly looses power and will not pull over 20 mph or achieve rpm over 2000 even in neutral! It has done this 3 of the 6 times we have towed the 5th wheel. The first mechanic cleaned the air flow sensor. That seemed to fix it. The second mechanic replaced the air flow sensor. That seemed to fix it. The 3rd mechanic has it now and is replacing the fuel filter housing. (This time the “replace fuel filter” notice was displayed). Fingers crossed! Any ideas as to what the likely cause of these dramatic losses of power might be??? Stuck in Utah!