weird shudder in park today

[YEGbluesilverado]

So driving the family to supper today in my 16 crew cab 5.3 nice hot 21*C day had the AC on and after driving thru some stop and go traffic for 20 min and getting to the restaurant I backed into a slightly up hill stall and pull forward to straighten out and back in again and we feel a slight shudder vibration.  I checked the trans temp it was 88C and sat in park with the slight shudder and checked my transmission fluid it was slightly below the hot section but i was slightly rear end high.  Came out to leave hour and a half later and could just barely still feel a slight shudder and it didn't get change with a rev of the engine.  I drove it the 12km home and it felt normal no shudder at stop lights after we left.  Im up to 106,000km and plan to get the transmission fluid changed and filter as I bought it with 72,000kms last april and am unsure now if the dealer did the transmission filter and fluid.  Any ideas?

[YEGbluesilverado]

ok this morning I had a tech friend scan for codes and nothing came up.  It was warm and about 3/4 quart low on atf so topped it up and the fluid looked clean.  No shudder since the one time.  going to drop the pan and replace the filter and some fluid this weekend.  also found a leaky transmission cooler line.

[diyer2]

Checking fluids is vital to avoid problems.

[YEGbluesilverado]

Dropped the pan and filter this morning slightly browner than red.  cleaned it all up and refilled its a hair smoother so thats nice.  what a pain to drop the pan though ended up jacking up the transfer case and lowering the exhaust like the sunday driver videos.