First the a/c stopped blowing one speed @ a time ( 1 wouldnt work but 2,3,4,5 would, then 2 went and so on ) now all inop...
Second cruise inop, "cruise" light in dash comes on interm. & blinks erratically @ times & continous @ times...
Third the fuel gauge pegged @ full ( car was running & I slammed trunk and I noticed yellow "low fuel" on & gauge @ E... Opened & closed again, went back to full)
I havent got into anything yet, any suggestions?

dont know about cruise but you probably have grounds for the tank sending unit in or near the trunk your going to have to find it and clean and tighten.

the a/c control module is probably bad, dont even go to the dealer cause there price on it isnt even funny. i tried getting one from the junk yard for 50 because my lights are out and all the ones there had those same lights out. i just took it back and am living with it. ive heard radio shack has the lights and you can solder them in but the thing was a pain to take apart

Fuel gauge is a bad sender, it'* very common in the 97+ w Bodies and 00+ H bodies. There'* a part you can buy and replace on the sender to make ti work again.

Hvac.. sounds like the resistor is bad, also common.

Unsure about the cruise.

Cruise might be a blown fuse, or a bad module. But all in all, it sounds like you have some corrosion problems. Has this car ever been flooded? Does this car have a fuse box under the rear seat? If so, unbolt it and look at the bottom.

Impalas dont have fuse boxes under any seats, but they do have them on the sides behind the doors. Those places are known to be places where water/moisture can get in the imps.

well he wanted the a/c fixed first for his wife & new born, so check blower motor(good),checked signal from control head selector switch(get 3.42v from a different wire as i change selector switch, also have batt voltage on a wire & a ground) believe resistor to be bad so i replaced it and still dont work.. at the blower motor plug on settings 1,2,3,4 i get 3.38v and 0 on 5 ?

this may help, looks like the speed is controlled by grounding through a variable resistor, seems you should still get a voltage difference when changing steps though. possible you got a bad one?

make sure you check your grounds to those modules too that will give you funky readings if there intermittent or corroded

One other thing seems to be common and that'* the ignition switch. Almost all the car'* power goes through it. Might be worth looking at.