I just converted my D-50 pickup to a 4d55, and have been driving it daily for about a month or two, put about 1,000 miles on it. So far, no complaints. Mine at least fires right up. Pretty good performance for a small diesel, and great if you get into the boost. Cruises around 70 with no problems, and has been getting me somewhere around 28 mpg ( mine is 4wd and I think I still have some tuning to figure out). As far as I'm aware, they aren't notorious for any serious problems. Hope that helps.

85 4x4 Pickup, 267K, 4d55 Conversion, Sway-A-Ways, Dual Batteries