'89 22re won't start

I have an '89 22RE that I am having a killer time getting started. When I turn the key I either get a single hard clunk, or the engine will slowly turn but not fire up (this happens both by clutch starting and clutch cancel switch). I have replaced the battery, both cables, starter, ignition switch, checked the engine bay wiring harness, checked the timing, ohm resistance in the coil and wires, and pulled out a lot of my hair. Does ANYONE have any idea what else this could be short of now ripping out my interior wiring? I would love to avoid redoing my interior...........

Why do you think it is the wiring? What's not getting power when it is suppose to?
Have you adjusted the valves? Does the motor turn easily when you use a wrench to turn the motor?
What do you mean by "clutch cancel switch" and "clutch starting"?
Without the motor running, how did you check the timing?

I take back my timing remark. Don't ask me why I typed that in. The starter is not getting enough voltage to turn at the normal speed, even though the engine does turn freely with a socket at the crank bolt. It's the drastic drop in voltage on the truck's voltimeter that is puzzling me. Normal starting drop has always shown around 8 or so on the gauge, now it drops around 4 according to the gauge. As far as clutch and cancel switch starting, the truck has a clutch cancel switch that can be used without pushing in the clutch to start. I get the same result either way I try to start. Sludge should not be an issue either since I have put on a new pan gasket, cleaned the pan and have fresh 10w30 in there.

How old is the starter? Old starters may have worn bushings that can bind and need a lot more power to force the starter motor to turn.

Unfortunately, the starter is brand new (no reman parts) and has only been on the truck for less than a week. I have tested and inspected the interior wiring in the starting circuit and found nothing yet. I will be trailering the truck to an electrical shop on Wednesday after not finding anything on my own. The diagnostic fee is only $35, and the tech there assures me he will be able to tell me what it is with certainty within a day or less. I will be sure to post my results in hopes of helping others in the future.

Well, I am happy to say that the wiring guru was able to help me out, and not only found the short (wiring within left fender leading to ground), but he has gotten my truck starting with no problem. However, once I start it, the truck sounds like I have exhaust trying to "backfire" into the intake manifold. The engine lopes and will not rev up when I hit the throttle. Would the valves need adjustment again being that it sat for over a year? I tried rotating the distributor to advance/retard the ignition timing, but it still sounds horrible in the area of the intake manifold. Anyone have any ideas/suggestions? Thanks in advance!!

Have you checked the air intake to make sure a critter hasn't moved in?
Have you put in fresh fuel?
Are the spark plugs wires properly connected?
Won't take you that long to check the spark plugs, cap, rotor, valve lash, butterfly valve in the intake, etc.