I have a 93 s-blazer 4x4 4.3 vore tech it has 300 000 klm on it. the problem is that the number 4 an 6 cylnder have next to no compreshion. it runs like crapI need some help

 

Sounds like you are going to be pulling off the passenger side head in the near future.

One more thing that you could check is squirt some oil into the cylinder and turn the motor over with the starter (all plugs out) a few revolutions. Squirt some more in and turn it over again. Then re-do your compression test. If the compression returns to normal, you have bad rings and you'll have to tear the engine down. If it doesn't, its either a head gasket issue (could be blown out between the two cylinders) or a valve issue that just so happens to affect both cylinders (i.e. an intake or exhaust valve in both cylinders that is not closing properly).