Hi I recently bought a 2000 S-10 ZR2 and had the same problem with the 3rd door. What I found was that the latch on the bottom had rusted shut and wouldn't release, so I used my Dremel to grind the bolts off of the latch and put a new latch in. The latch is held in by 4 bolts in the bottom of the 3rd door. I also put new stainless steal bolt's and washers in.
I must have really got lucky with my 2000 ZR2. I bought mine in May of '06 and it had 152000 kms, it now has 227000 kms on it four years later. This truck has been awesome!
The only problems I ever had with it was the steering fluid oil cooler is way up front in the grill, and when temperatures drop to any lower than -35 or so the oil gels up and blows the hoses off. So we just bypassed the oil cooler (works fine now). The interior is starting to get some squeaks and rattles, but that's to be expected of any vehicle with that many kms. The 3rd door handle broke off as well, but the day it broke the temperature was down to -45, plastic doesn't do very well at that temp. Actually, my friend's 3rd door handle broke on his 2000 S10 2wd the same day.
It may not be the ultimate 4x4 for hardcore wheeling, but it still handles better on gravel roads than a lot of brand new trucks do, gets OK fuel mileage, traction is great on ice covered highways, and with a good set of all terrain BFG, it'll tackle some fairly deep snow.
All of you have had bad luck. My 2000 S10 ZR2 3 door has 215,425 miles on it, and only replaced a fuel pump on it, with only normal wear and tear items on it. She still drives every day back and forth to work. About to replace the wheel bearings for the first time, and replaced the rotors just recently for the first time.
And for anyone that doubts it, I have had the truck since new. Rather have this truck than any other make or new trucks. I pull a 18 foot enclosed car trailer with cars or 3 Harley's in it. It has had more trailer miles on it than without. Do that with a Ranger, Tacoma, Dakota, or any other, and watch them drop like flies. Also does moderate off road during hunting season.