my guess is that the radio is on its last legs. You can find replacements on ebay, (ones that others have pulled just to put in an aftermarket deck).
For tearing out your dash, take the two 7mm screws out of the gauge cluster area, there are above the column. then unclip either side of the dash. unplug harness as you come to them, one for 4wd (if equipped) one for headlights, (think there are three total on drivers side. next, put the column all the way down, then pull top part of dash cluster out from under the overhang. until it is free. then, carefully, pull bottom section of dash and gently lift it over the hazard switch. will have to pry it some. take out the four screws holding the heater controls, then the four that hold in the radio.
Pull radio out of dash, disconnect the antanna wire, and the plugs for the radio istelf. if you are installing an aftermarket cdplayer, take out the 3 10mm nuts that hold the factory pocket on the radio.
Take the new cd player out of the cage(silver sheath that is around it, usually by prying little tabs on each side of the cd player). mount the cage into the new dash kit, and bend down the little tabs inside of the cage, to secure it to the dash kit. Push tabs you pulled out to release the radio back in, actually, push them in a litle farther that they were to begin with. Set aside.
Take wiring haness, metra part number 99-1858, and connect wire for wire(color for color) in each harness, above listed part and one that came with the radio. Use crimp caps, (butt connectors, whatever) I don't use tape, not secure enough. Ignore the orange wires, should be two in one, and then ignore the blues, as they are for power antenna. Set aside.
Take antenna adaptor, metra part number 40-GM10 and attach to factory antenna wire.
Mount the assembled dash kit in the dash, and connect the wiring harness to the factory wiring. Pull them through the cage on the dash kit, (along with antenna wire)
Mount everything back in, put the dash back in , reconnecting all harnesses you pulled out in earlier steps. Then, when everthing is back to looking original, plug radio in and antenna wire, and test system. if all works, push radio into dash, untilit clicks. Done
also, check out this site, the stap by step is pretty much the same, except that you don't have to lower the knee bolster, and there are two screws above the cluster.