Is your exhaust up to it, no restrictions, silencer blockage, the 2.5 has a bigger bore. The RR difs will only give the potential of another 8-10 mph your engine should be up to the job.
The easy checks I would do
Fuel pick up clean?
Fuel pipes correctly fitted, meaning feed and return in the correct way around.
Lift pump ok
Fuel filter ok
Air filter ok, also no restrictions in the air intake, I have seen rags partially blocking.
Valve clearances, not too tight, rocker arms not pitted?
I have seen the crankshaft bolt come slack and cause the crank belt pulley to wear retarding the timing.
Assuming the engine is mechanically sound, compression etc
Your fuel system, injectors & injector pump overhaul, costly though.
The easy checks I would do
Fuel pick up clean?
Fuel pipes correctly fitted, meaning feed and return in the correct way around.
Lift pump ok
Fuel filter ok
Air filter ok, also no restrictions in the air intake, I have seen rags partially blocking.
Valve clearances, not too tight, rocker arms not pitted?
I have seen the crankshaft bolt come slack and cause the crank belt pulley to wear retarding the timing.
Assuming the engine is mechanically sound, compression etc
Your fuel system, injectors & injector pump overhaul, costly though.
