92 cultass 3.4 L 5 speed boggs down at 3.5 grand

I did have this car up for sale but decided to keep it. I had put the felpro intakegaskets in it they fixed the vacuum problem. It ran like a brand new car that night. But now for some reason it is starting to act up. You have to shift before 3 grand of it cuts out. Any Ideas? I will probably be putting this car up for sale in again in a couple of months. I am using it temporary, and I want to make sure it is running sound. Its almost there. this is a very fast and healthy motor it runs great when it feels like it....

[email protected]