Do you have any concerns about your current truck - engine, trans, etc? If not, IMO put the money in the bank that you'd spend to upgrade to a diesel and keep driving your current truck. The added tow power of a diesel is nice, but it's unlikely the difference in MPG will amount to much (unless you tow A LOT) plus the maintenance of a diesel is higher.
Sherm & Terry w/rescue Eydie (min Schnauzer) & Charley (std Poodle)
2015 Jay Flight 27RLS (Nights Camped: 102 '15, 90 '16, 80 '17, 161 '18)
2006 Ford F350 6.0 PSD, 4WD, CC, LB, SRW, Camper pkg, Equal-i-zer, GY Endurance (E)