P305 and dissapearing coolant

I have a 99' 2door 4x4 Tahoe, constantly getting check engine light. Replaced both front O2 sensors (bosch), replaced plugs (), and wires (bosch), paid $175 for fuel injection cleaning. When I tow is when the light comes on now its a P305 which is a cylinder 5 misfire, I really dont want to pay the mechanic another $75 Ive already had to pay $150 for two diagnostic readings. Another problem Ive noticed is the coolant reserve seems to evaporate or dissapear, there is never any antifreeze leaked out anywhere and the truck never runs hot, but this bothers me.

i'm no expert, but i may be possible you have a head gasket leak? coolant could be going into #5....

its funny you say that. I was going to include that I had a leak, but didnt think it would have much relavence so I didnt, I really dont know much about cars, but with you not knowing I had a leak thats my next fix. Now I just hope there is no damage done !

also check this forum for "smell anti freeze"...they talk about intake gasket leaks there and some other causes....