help - 80 series performance

I was hoping someone maybe able to help with my performance problem. I have recently bought a modified dual cab 80 series 1997 ute, and over the last 2 months its performance has decreased on highway especially up hills and around town - it's like its lost a whole gear. It has done 150k and the injectors have not been done yet, would they be due? I have checked my snorkle and it is clear and my air filter is ok. I have also replaced the fuel filter and dropped fuel out of both tanks and they were clean. I bought some of the C.E.M Flushing Oil Concentrate and ran it through my engine proir to its last oil change and have been using CEM cleanpower in the fuel for the last 600kms and no noticiable effect. I was maybe thinking pump timing (hopefully not the pump itself) - any thoughts????

Gearbox dramas:
It also has a clicky grinding noise when at idle which dissapears when the clutch is depressed?? The most annoying thing is its whining noise when in 1st, 2nd and slightly 3rd when acelerating and especially decelerating, say around a corner at a certain rev range (low). I don't have a tacho so I can't specify. It sounds nasty but a mechanic said nothing to worry about, just old parts on new. It also hops & shudders when taking off in 1st and especially reverse and especially under load, one mechanic said its just the cruisers and another said a pitted part?? in the gearbox that is gripping.

Any ideas would be greatly appreciated... - this ExplorOz forum is awesome!!!