No cruise control available light comes on, and when this sign appears cant rev the car over 3K rpms driving on highway, going down hill and foot of the pedal light will come off

I suggest check the easy things first. Vacuum lines, could cause a lean condition, fuel filter restricting the fuel flow lean condition. Carefully clean throttle body with proper cleaner. I'm a shade tree mechanic but these simple things work sometimes. You didn't mention if you have the cvt trans. If you do and you are going 75 80 on the highway coming to a hill will cause it to race that high. Then when the hill is crested it will slow down, I don't like it either but it is the nature of the beast. I often cancel the cruise on big hills on the highway so it doesn't do that.

First I'll assume you haven't read the owners Manuel, Cruise control is not perfect on any vehicle. if coming to a hill put foot on gas to help rpm, going down hill put foot on brake to keep same speed, cruise control operates off of engine vacuum. Speed sensors can be affected by putting on smaller or bigger tires than what is on drivers door.

Sounds like your transmisson is going, i had the same problem.

the very first thing you should do is have your fuel pressure checked. sounds like fuel filter or fuel pump.

mass air flow sensor its in the air intake pipe

I had the exact same problem on my 04 GC. I put some Techron Concentrate Plus Fuel System Cleaner in from Wal-Mart and it seemed to fix the problems right away. Let me know.

THERE IS A TEMPERATURE SENSOR ON MOTOR WHICH CAUSES THIS PROBLEM... USUALLY IT SHOWS A NEGATIVE TEMP READING WHICH CONFUSES THE COMPUTER CAUSING IT TO REV UP....HAVE THE ENGINE DIAGNOSED ON A SCANNER....GOOD LUCK...

it's getting to much egr the egr has gone bad and needs replaced.
the diaphragm in the egr is leaking, and default position for air is defrost.so when you hit 3000 rpm you don't have enough vacuum.

What is your speed at 3k rpm? What rpm would you estimate was previously 'normal' for highway cruising? If your Lexus is auto trans, it could be two things, it's either not shifting into the highest gear, or it's possibly slipping in gear (although I would think that would cause the rpms to fluctuate, not stay at a steady 3k). If it's a stick shift, again, it could be clutch slippage, but my choice from your description would be not shifting into the highest gear. Bring it up to highway speed slowly, counting how many shifts it makes, I.m guessing it's a 5 speed auto, but I'm not sure about that.

Simple answer, no, it will not most likely cause any increased wear to your engine or transmission. Yes, it is normal for the engine to rev while climbing a hill while in cruise control.

The cruise is designed to be used on flat (or semi-flat) stretches of highway at 55mph or higher so you don't have to hold the fuel pedal the whole time and your foot doesn't get tired. The cruise control system will try it's best to keep your vehicle rolling at the set speed, increasing/decreasing the throttle to compensate for changes in engine load.

If you are driving with cruise on, try lightly putting your foot on the pedal and you might notice that the system will actually move the pedal itself. If you are in cruise, and you come up to a large hill, try putting your foot on the pedal and getting it up the hill on your own w/o cruise then resetting cruise once you are off the hill.

Also, cruise is not supposed to be used in moderate/ thick traffic or on country roads with a lot of rolling hills. The cruise control system is a "dumb" system meaning (not that it's pointless) but it will only change the pedal as the speed changes and it has no idea what's coming up next, even while you are already on the hill.

So, it is normal operation of the cruise control to try to compensate for a hill by constantly revving up the engine and letting it fall back down to try to keep moving at the exact same speed you set it for. If this is a bother, you can always use your foot to hold the pedal while climbing the hill normally.

Don't worry, it won't cause any increased wear and tear on your vehicle. I hope this helps. Good luck and don't forget to rate! Thank you!