hello. if it's reliability that you want then you are probably best to stay with the q-jet. they are as reliable as you can get ,but on the other hand you could change it out to the eld'y and it's also a good carb. it all depends on what you want for the truck.you may want to check your valve springs as you do the job at hand.. and i also agree that you may be in to a overhaul with that milage. if you go for the change of the carb then stay around 600 cfm on the carb. good luck and wecome