**Help**Engine keeps misfiring,'97 Monte Carlo.

I have a '97 Monte Carlo ls with 92,000 miles.I keep up on all maint.Problem started in January and still is not fully resolved.When starting,engine will misfire causing Service engine soon light to come on.Car will run very rough (like when spark plug wires are mismatched).After about 3 minutes car will smooth out and run fine.Dealership found dirty injectors,and relpaced o2 sensor and a hose was loose under the manifold.After that it was fine but problem still happens.Nobody can figure out why and are telling me its bad gas passing through injectors.I love this car too much to trade it in.Can anyone help?Thanks!!!I use injector cleaner every other fillup.

You may need new plug wires and plugs if you havent allready changed that.. That I would change. The other thing to check is your coil packs. Depending on your engine, you have 3 or 6 of them. Your catalytic converter can cause this type of problem or any other exhaust blocker.