For what it's worth, here's my opinion.
Pre EPA diesels are in demand. A 10 year old diesel may fit in that category (Pre EGR/recirc and DEF systems). About 2003 they started to play with the diesels and some manufactures got on the band wagon sooner than others. I would figure 300,000 miles off a pickup truck engine. The body normally rots out before the engine dies. I'd talk to your mechanic and have him look it over. Oil changes cost more since you have about 4x the oil in a diesel engine but you can get longer oil change intervals. (My pickup holds 4 gallons and my semi holds 11 gallons.) Oil samples are GREAT. Lets you know exactly what's going on in that engine. You have blood tests, the engine has oil tests. Have not heard anything bad about the Chevy diesel on the boards but talk to your mechanic. I don't use dealers. I have a diesel mechanic that specializes in pickup diesels and I use him to maintain my pickup. I can call and schedule an oil change and wait on it or I normally drop it the night before and pick it up when I get off work the next day. Sometimes he'll find something else like a bad seal, since mine is a 2004 and have to hold it an extra day. Last time I had to replace the transmission cooler lines.
On the plus side diesel are great for towing trailers, get better mileage, go longer between oil changes 5,000 plus miles. New engines, the computer tells you when to change the oil. (40-50,000 miles on my semi, based on oil sample results). I change my pickup every 5,000 miles just to be on the safe side but many people go closer to 7,000 miles. Point is, people buy diesels because they have a need, not because it's cheaper. Right tool for the right job.
According to
http://www.equispirit.com/info/articles ... tterms.htm Tongue Weight - The amount of the trailer's weight that presses down on the trailer hitch (tag-along) or the rear axle (gooseneck). Too much tongue weight can cause suspension/drive train damage, and can press the vehicle down in back causing the front wheels to lift to the point where traction, steering response, and braking are severely decreased. Too little tongue weight can actually lift the rear of the vehicle, reducing rear-wheel traction and causing instability which may result in tail-wagging or jackknifing. On trailers over 2000 lbs. tongue weight should be 10-17% of trailer weight. For gooseneck trailers, tongue weight should be 25% of trailer weight.
So you need to find out the tow rating of the RV but I suspect it's only rated for 5,000#. You also need to weight the RV and find out how much trailer tongue it can handle. A 5,000# trailer will need about 750# tongue weight. Don't know how big your horse trailer is but I looked at a couple of 1 and 2 horse trailers and it might work.
Good luck and if you need me to look at some numbers I can.