Just had leaking radiator repaired at local shop. replaced radiator and drove truck and noticed a brief shudder in 4th gear that is intermitten. when shift into 3rd gear manually the truck does not shudder. put back into 4th gear/overdrive will get intermitten shudder for 1-2 seconds at steady speed. IF I take my foot off gas when shudder starts it stops or if i manually put it in 3rd it does not occur. I can start out with gearshift in 3rd and transmission shifts fine with no shudder. Any help greatly appreciated.