98 GMC Envoy - No Power? Intake Manifold or Converter?

[scootsville]

Can someone please give me an alternate opinion?

I went to one mechanic and he told me what was going on with the car. I called another to get a price estimate and he said he's never heard of this happening. So, I'm confused. What's your opinion?

Background:

My car isn't getting much power. If I try going up hill, I'm lucky if I get 25-30mph. If I step on the gas to try and get more power, the car will sometimes start to jolt like it's trying to get the power but can't.

I took it the mechanic and he said the lower intake manifold gasket is leaking antifreeze and shit into the exhaust and that is clogging up the catalytic converter which is why I'm not getting the power.

The mechanics exact notes, are this:

"We checked codes and found fault code P0440. We checked for cause and found that the gas cap holds no pressure and leaks. Need to replace cap to eliminate evaporative leak. We noted that the intake manifold is leaking and needs replaced. This may cause a problem with air fuel mixture. This appears to have been the case as the catalytic converter is melted internally and has plugged exhaust. This is the cause of no power. We recommend replacing the catalytic converter and intake manifold gasket and then rechecking engine performance."

The other mechanic I just called said he has never heard of the intake manifold leak causing the converter to get clogged.

Does anyone have an insight?