1997 Other Chevrolet Models I left my truck sitting for 12 d

First, I love this site thank you! My c/k class 1500 Chevy truck got a new engine at 126,000 mile mark. I bought the truck through a private owner and for the last 4 years has been working great other then the engine. But I went on vacation for 12 days and about 5 days ago I came back and found a fresh puddle of deep red fluid which matched the transmission dip stick about a hand palm size big. My fluid level was o.K when I drove it home about 3 hours away and again the next day when my engine was running warm ( 210 on the gage) but, then the next day when cool the level appeared low.
With no leaks noticed, and no indicator lights what am I looking at? Thank you !