sorry, i took it as you dont go over 4000 rpm because you loose pressure. if its because of mechanical issues that you "VARY RARELY go over 4000prm" maybe you should take it to a mechanic and get it looked at
the only time i pay a mechanic is to do a wof, i prefer to do everything else i can myself and when time allows ill get to looking at my problem, i didnt come on here to moan i just stated that the t/a problem sounded similar to mine so it gives me somewhere to look first