My 99 Suburban shakes violently when climbing- I usually have to slow down to 50-55 mph. It feels like the engine is about to drop out of the Suburban. The service engine light ALWAYS comes on when this occurs. After a day or two, the light goes off. The dealership said the pistons were probably missfiring-tested it-they work fine. No one seems to have any answers, and it has gotten worse!!!! I have read the previous posts regarding this problem, but if anyone has anything new or different- it would be greatly appreciated! Thanks :banghead:

probally what is happening is the valves are sticking in the guides causing your misfire and lack of power.
This usually occurs when the engine is hot and is under a load (highway speeds, climbing hills).
I would check for proper operation of the fuel injection system and the secondary ignition first, but I would say most likely the heads are going to have to come off

Our '94 did that( like it was kickin back) after a tune up and I thought it was the tyranny. Turned out one of the spark plug boots had come off a plug. One my son had done. So check all your wires and plugs also.

I had a '99 do that with a 5.7 engine. Tried plugs, wires, cap & rotor but the P0300 random misfire kept coming back & it would still start sputtering up long hills. I was finally told by GM to try the fuel injectors (supposed to be a fairly common failure). Not knowing which to replace @ $55 each I took off the injection connector by the throttle body, tested each with an Ohmmeter & found all read the same. So I cleaned & applied dielectric terminal grease to the connector & haven't had the problem since.

Dorp a post when you get it fix. I would like to know what was wrong. Thanks Dave