fuel pressure, maybe even a bad pump, check out them injectors... sounds like my car did when the fuel pump was goin....but it deff sounds like a fuel prob to me..... check the pressure it should be around 14-15 i believe for a 350? anyone correct me if im wrong.....

Get a fp gauge on there.

Sounds like your running way lean.

And if it is a vac leak causing that..its gotta be one hell of a friggen leak. ;x

Not to say tho it cant be a combination of things going wrong. Fp going..in addition to a vac leak.

Also no one mentioned it..but check the filter.
May not have been changed in some time, and its real easy to clog up now. If the filters real old, it may have some moisture in it, which now, with the Ethanol based fuel we have here, will pack up solid in no time. You wouldnt beleive how many drievability probs we have fixed at work as of late with fuel filter changes. Some of these things you cant even blow through.

Also you bought the car running like that i assume from some guy. he hasnt had it out on the road in awhile i bet, and obviously you havnt either..how old is the gas thats in it?

Id look at bad gas, clogged filter first, then check the fp so it'll be accurate.

If the filter is packed solid tho, a pump may be in your future from all that time pumping against such a high resistance. ;x