loss of power and retarted timing in 1995 silverado

[texmister2010]

i have a 1995 silverado with a 305, i have checked several things, changed the mapp sensor and checked vaccum lines and changed the air intake valve, but i have suffered a huge loss of power, shifting is slow (automatic) and my timing wont stay where it should be, i was curious if anyone had any tips on what else to check and im thinking it might need a new timing chain but before i get to tearing apart id like to know any other ideas, thank you!

 

[zora]

Do you have a check engine light on? Are you checking the timing with the PCM disconnected? When you check the timing is the mark bouncing around? Have you checked your vacuum reading and if low have you tried disconnecting the exhaust before the catalytic convertor to check if it is clogged?

 

[Chuzz]

I'm thinking like Zora about a clogged cat con or some other exhaust restriction. Disconnect your Y-pipe from the exhaust manifolds and check for power.