After having my Cummins, I feel like I'd never have a gasser again . . . but if I did, I think I'd have to recommend the 1/2 ton Chevy. The LS engine platform is kickass, and they'll run like a raped ape. I took the heads off my Brother's '99 last summer at 135K miles and the cylinders looked like new, for what it's worth. I only had the heads off because of broken exhaust bolts that were caused by a warping exhaust manifold. They were not leaking, but brother had extra cash and wanted them fixed. From what I've heard they took care of that problem.
Jackass totaled the thing right afterward.
Honestly, 25k will buy a hell of a truck . . . I'd get a 03+ cummins . . .
for example . . .
http://cgi.ebay.com/ebaymotors/Cars-Trucks___2005-Dodge-Ram-2500-Quad-Cab-SLT-4WD-Cummins-Diesel-SB_W0QQitemZ380078794254QQddnZCarsQ20Q26Q20TrucksQ QddiZ2282QQcmdZViewItemQQptZUS_Cars_Trucks?hash=it em380078794254&_trksid=p4506.c0.m245&_trkparms=72% 3A727|65%3A12|39%3A1|240%3A1318
I know you said you wanted a 1/2 ton, but this thing will last forever and never leave you wanting for more power. I'm just another dude who drank the koolaid though. hehe.