Not knowing very much about the truck - I can only assume it's 4X4 with this and the std cab & 8" bed and mileage you mentioned. NADA puts the final value (after deduct/adds - noted below) at $10,750 low, $12,200 avg and $13,250 high. The high mileage dropped the value $1425, there's an increase of $1575 for 4X4 and an increase of $4525 for the diesel. NADA had no specification for 12 or 24 valve. Of course those numbers are for a zip code of 19047. Go to NADA and enter in all the data you have using your zip or the zip where the truck is.
I figured since I did NADA for you I may as well go to KBB (Kelly Blue Book) so here goes:
KBB didn't think as highly of our old truck here. I allowed everything that came up in the default settings (ST, Cassette etc) and made sure I selected 4X4, it defaulted to auto. However, kbb provided a choice of 12v or 24v. So Excellent condition $9920, Good $9180 and Fair $8235. Oh these figures were "private party values".
Go to the sites I mentioned "NADA" and "KBB" - plug in as much info as you can find available, and they are only a "best guess". It really comes down to the truck. I used both of these sites when I sell an auto or, the one with the higher price if there's a big difference.
Using my truck as an example. In May 01 found it on line (bone stock contractor trade in) at a Chrysler dealer in Yorktown Heights, NY, it had 75k miles, Firestone Steeltexes and Monroe shocks. Dealer listed it at $19900, I convinced them down to $18000 and they had to fix a few things brakes, 2 new tires, touch up and so forth. NADA & KBB listed it $22 low to $26 high - so like I said it depends on the truck and timing is everything. Good luck to you. Happy hunting!