I have a 95 Jimmy 4.3 4x4. It started bucking when I let off the gas. My mechanic said it was losing approx. 8% pressure and replaced the fuel pump. It didn't solve the problem. Now he wants to replace the timing chain which he said is a 7 -8 hour job and big bucks. Does this sound right? He did a diagnostic test which didn't show anything. Would bad injectors show on diagnostics? What would be the proper process to eliminate possibilities before I keep spending money

If this bucking occurs at an idle it is the egr

The 1995 Vortec are bad for bad carbon deposit in the EGR Valve. Remove it and clean it with carb cleaner or injector cleaner from a can, spray the carbon away then spray some silicon lubeacator from a can before re installing it. Good luck oh and check your vacum lines before you get your hands too dirty.

Egr or mass air flow or last but not least map sensor

To see if it is the EGR Vallve remove it clean it out and reinstall it it should only take you about Half hour

I had the same problem; it could be one of two things: First check the Enhanced Distributor Ignition Systems (EDI) a simple check. If that's not the problem then remove the intake manifold. Check both the presure and return fuel lines under the manifold. More than likely they have rubbed together creating a fuel leak.

It will not be the timing chain.Is check emgine light on?I would try another shop to scan computer.