Recently I had my clutch replaced, installed 4.785 FD and FPR adjusted, it was at 53PSI before and it was running too much fuel.

currently I don't have a speed sensor since I replaced my LSD to a different LSD. and the new LSD requires a new speed gear.
Therefore, Engine Light on, no speedometer and no vtec.

Heres the problem, i was on highway today and riding at approx. 5000 RPM, but the weird thing is everytime I was in 5th gear and pass approx 5500 rpm. the car felt like no power at all even I full throttle it. The car just had no response at all instead of RPM dropped slowly. So I had to shift to N and let the RPM drops under 5000 RPM, and shift back into 5th. I've already set my Vtec point to 7000 to prevent vtec kicks in with engine light on.

Then I tried to stay in 5000+ rpm in 1st, 2nd, 3rd, for 20 secs. no problem at all.

What could be the possiblies, such as. fuel pump? throttle cable? TB? Fuel? Engine Oil? what else?

 

Your VTEC is not engaging. VTEC has certain prerequisites in order to engage. Speed being one of them, and you not having a speed sensor is the main cause.