Here's what I think
In 1998-99 the truck would cost about 36-37K out the door. On 5 year Depreciation:
New 1/1/99 - 37,500
Value 1/1/00 - 37,500 * .8 (5 yr. depr.) - 30,000
Value 1/1/01 - 30,000 * .8 - 24,000
24K plus dealer markup is about $28K. However the truck is basically 3 years old now, and out of warranty.
For not much more money you could get a new one. Financing will be easier and at a lower rate. You might even find a 2000 leftover with a rebate or lowered price. I shopped a 2001 F-750 Single axle dump, and was offered a pretty good sized rebate or 8.9% financing.
Bottom line is that if you NEED the truck then 29K is money well spent for what you need, NOW. Otherwise you can do better. The upside is that taxes will be a little less, and if the truck has easy miles on it and you keep it nice, it will last for a while.
Now, my opinion is based on our situation. If this is your first newer truck, then it might be good way to go. This sort of deal is exactly what I bought when I couldn't afford new, but needed reliable. Now we have other trucks, so I have time on my side when shopping.