WHen under load the motor revs up and it seems that the Clutch is slipping, it has 100000miles and I suspecting the clutch or the high / low range might be messed up, its a 4 plus 3 manuel transmission.

YOU DO NOT SAY WHAT TYPE VEHICLE OR YEAR BUT I WILL TRY TO HELP,IF IT ALSO SLIPS OR CHATTERS IN HIGH GEAR SUSPECT CLUTCHES, HIGH GEAR AND REVERSE OPERATE OFF THE SAME CLUTCH PACK

If engine revs increase but road speed does not increase, your clutch is coming to the end of its life and needs to be replaced

seems a bit early for clutch. how many k's? I would start by checking the intake tube for splits & security & airflow sensor. they will cause the engine to rev but no response (like a slipping clutch) so its manual right?

Yes it is the clutch slipping, in high gear the greatest load is put on the clutch so that is when they slip the most.

It does sound like a clutch, but deserves to be more thouroughly checked out, Does the clutch pedal feel normal? is there a little free-travel at the top of the pedal stroke? do you see oil dripping under the car?
Clutches usually go out slowly, they start to slip under heavey load first, then gradually slip even under light loads in low gears. If an axle was loose, it could have spun in it's hub, with the hood open ans an observerstanding beside the car looking down at the axles, slowly let the clutch out (engine running, in reverse gear, ) being careful not to hit your assistant, if the axles turn- one of them, but the wheel doesn't this is your problem. If the axles don't turn with the clutch out, and engine still revs, well it's time for a clutch or transmission, Good luck, hoe this helps

If the clutch slips, the clutch disc is worn out. The clutch hydraulic system only "disengages" the clutch.

it could be possible that your clutch is slipping at high revs,depending on its age[wear and tear].does it also slip under normal driving conditions?if so then it needs replacing.to change the discs to ventilated,the brake pads are different and the brake callipers need to be changed..cheers

Since you did not say what type of transmission you have i will suspect the clutch is slipping if it's a manual.
If it's an automatic, it could be several things. Low fluid level...clogged filter, fluid needs to be changed..transmission serviced...weak pump, bands/clutch packs worn...etc
Good luck..i hope this helps, please rate me a fixya.

I think you will find the clutch plate needs replacing. Your symptoms sound like a slipping clutch. You will need to take it to a mechanic, this is not a job for a handy man.

The grinding sound may be a throw out bearing or the pilot bearing. The sticking throttle problem sounds like a linkage or cable binding up from possibly damage due to the impact from the accident.