2002 Chevy Silverado coolant leak

Had starter go out in December, had car towed, before it was tolled, the guy said he would tap on starter, he used a pipe and 3 # hammer and was hitting very hard at night when it was dark, two weeks later my coolant light came on, my thought was he maybe missed the starter and was hitting my block, I was inside the truck, used about 2 and half gallons in around 800 to 1200 miles, took it to two places and it held pressure, but the first time engine was hot and second time let sit for 2 hours, still held presure, put uv leak detection in coolant, still nothing, I think it only leaks when cold.Checked for ul solution in oil, when I removed oil cap, I see nothing in the oil. Any ideas Jeff PS temp is good and see no smoke in tail pipe