A Body Stalling at Idle

If the intake gaskets were leaking from the lifter valley, I think you would see oil burning as well, as it would suck oil from the lifter valley into the intake ports.

Here's another thought...have you checked all the vacuum hoses? Could one have developed a crack or a leak?

Can you turn down the idle to 4-500 rpm in neutral (what it would be in Drive), and does the engine stall then? If it stalls, then its not the trans. If it does, then I'd suspect a vacuum leak from somewhere.

Also, have the idle mix screws been disturbed lately?

Just my $0.02