Not sure what constitutes 'much', but 23yrs after buying it new, the D21 I have has been pretty useful...and still gets 29mpg going over the pass. It'll do anything you can ask of a small truck, and make more power than the ford 4.9l six...which may be reliable, but struggles to pull anything worth crap once the road turns uphill.
Interesting Berto. Which engine do you have? 4x4? Manual trans? I know the ol ford 300 runs outta wind after 2k but hen its geared right it'll pull anything. Straight sixes are built for torque and longevity. I'm gonna get me an old truck soon and I hadn't given the D21 much thought until I read your post. When I say they won't do much I'm thinking of pulling 3500 lbs w/ 1k lbs in the bed.
Also, IIRC, you are a fellow lcr guy. Ive carried mine pretty much 24/7 since I got it 2 years ago. One of the best edcs IMO. I look forward to hearing from you. Damn, 23 yrs of ownership is a lot! I hope its nearing 300k by now. Take care,