Quick question, you said the truck has 110k on it, have you done a timing belt and water pump on it yet?
In my time at Toyota, doing timing belts, majority of the time during disassembly I would find the water pump leaking, usually 9 time out of 10.
On the 3.4l it is really hard to see because the fan pulley being right there.
When I first got the truck I always had a slow leak but didn't think anything of it cause it wasn't overheating or running well just as you described, when it finally came time to do the belt, during disassembly I found that my pump had definitely been the cause for the slow leak.
Keep and eye on it and see if it persist.