You need to remember...Oil is thick when cold..the colder the thicker(to a certain point of course),at any rate that short of a trip doesent give the oil a chance to heat up and flow properly...Thusly the sludge issue.I know with fuel prices the way they are,that this suggestion will hurt,but you need to let the truck run,and warm-up about 10 minutes (at least)prior to driving it.This will give the oil(and engine coolant) ample time to warm up,and pretty much eliminate the sludge problem.