an absolute 2 mic solution could be a mess. but if you keep filters it would be ok.
i run used filtered oils generally at 20-30 percent mix rate to keep my costs below regular unleaded and get the mpg bump. green says its a bad idea to run such blends through these, which is a big negative.
my tuck at its lowest weight is 5850 ish empty.
with normal road tools, full size spare and jack it is over 6 k. i assume you have a spare and ect normal tools inside? i rarely seen a steel wheeled truck under 4100 in ext cab 4x4. theres guys that say they weigh 3500.....
4-5 k weight with good gearing the little dub diesel i think is fine if your not towing. getting into the 6 k with big tires like my fat bastard its past any return i would bet for economy.
the 3550 and a 241 or s10 case would be a good combo. adapting to the ford speedo should only take a call to a place like dakota digital....possibly just use the gm sensor and reset the psom with thier 8k device.