Yay, It Worked!
When I got up this morning, I informed Tripp that tonight my phone was going to go beep beep (which is what we say when our alarm clock goes off), and that when it did, it was going to be time to turn off the TV and get ready for bed. So off it went, and I let him finish watching one of the short episodes of Thomas the Tank Engine, while putting on jammies. He didn't like the idea, but I invoked threats of turning off the TV and time out in his room, and it was a short-lived tantrum. He then picked out two stories while I made up his bed on the couch near the a/c (his room gets too hot in the summer), and after a snack and getting ready for bed we got through the two books. Lights out and he was asleep within seconds. Now to just keep this up every night and make it routine.