i put 50,XXX plus miles on an 89 LWB 1/2 ton towing cars all over the country. mine had 3.55 gears,318/auto overdrive. i added a 14 in. open element breather with K&N filter,160 thermostat,pacesetter shorty headers,no cats, 2 1/4 duals with 40 series flowmasters,truck got 13-14 mpg running 80-85 with a 3500 pound car in tow across kansas, stayed around 11-12 mpg in the mountains. the truck would loose 10-15 mph on a big hill,but i never had a complaint with it's power.truck had 185,XXX miles on it when i sold it. of course,now a 12V cummins handles those duties for me,and i have never looked back.