My 2000 Silverado will skip or shudder when I'm pulling a trailer or just going through hilly country. When towing I use the tow/haul feature and usually set the cruise at 60 mph. If I encounter a hill where my speed drops back to around 50 mph the ship/shudder starts. When the transmission drops to a lower gear the skip/shudder quits or is not noticeable. No problem on flat terrain. I have changed the plugs and wires but the problem continues. Would appreciate any ideas that would help solve this problem.
Thanks

It could be one of a few things, one being maybe the TCC solenoid is acting up. Does it feel like the engine is missing or does the engine run smooth but it feels like it is in the trans? It could also be time to change the fuel filter and clean the injectors.