I have a 99 Silverado new style, 5.3 auto 2wd. I believe it is a 4L60E transmission. The truck has 96K miles. Ive never had a issue with the transmission until recently. The other day it started upshifting harsh like it was in tow mode but wasnt. Maybe even harsher than tow mode. The next day it did fine and shifted normally. Then three days latter when I engaged reverse and backed up it felt like it was shuddering a little but then the upshifts were normal and it only did this one time in reverse. It has worked fine for the last three days. The fluid level is correct and the fluid looks fine and doesnt smell burnt. I have no mil light on either. I thought I would maybe drop the pan and check for debris first or is there something else I can check before this? Has anyone ever heard of any of this happening before?