by the way found out why blazer was always bucking. when i unhook the egr the engine light comes on but the rig runs perfect, plug it back in it takes around 400 km for it to start acting up again. my latest ? is when i connect the vaccum hose going to the the the transfer case the actuator to engage the front end sucks in right away even when the button on the dash is in 2wd? what does this mean ? is the tri switch broken or is the selector switch on the dash not working properly? i have the actuator temporaily taken up from under the battery so i can see what it is doing.

 

Your problem with the 4wd is caused by a faulty vacuum switch in the transfer case.