I have a stock 2002 5spd. Runs smooths and feels powerful under no load. Hook up my 8000 lb trailer and it tows fine until I hit 45mph then she struggles. Sounds like the turbo stops whining and like the engine is miss firing much like a gasser would. I have 8-10psi fuel pressure wot but no other gauges. Fuel filter is changed regularly. Any ideas? Thanks