Sunk my ride the other day so we pulled her back and ran about 5 oil changes thru her and then loaded her with Castrol Syntec Blend 20W-50. Runs great except the es want shift into the upper gears until she seems to warm up. Is this from the oil or could it be a ligering problem from sinking her? Took to the dealer for first service and valve check, he said he couldn't get it to duplicate the missing shift, wouldn't you know it! Anyway, what do you think? Should I just replace the shift module or change oils?