2004 Dodge SX Car loses speed then revs

About 3 weeks ago I had a transmission line blow out that goes into my radiator, that was all replaced and I was told my transmission was fine. I had no problems until last weekend after I had it in for an oil change and service. I had them check what the other mechianic did and they replaced a clamp that was loose and undersized. Last weekend while on my travels it began dropping in acceleration then jumping back up and droppping agian. I pulled over a few times and then continued on with no problems then it acted up again. At one point I noticed my engine coolant was below add, I filled it up after getting home and this weekend didn't have a problem until driving after nearly 2 hours and my engine light came on. What could be the problem? To let you know I travel 2 hours to visit family on the weekend, this doesn't happen until I come back the next day after using my car to only travel around the city. It usually sits for a few hours before I leave. Any information you can give would be helpful.