Taking the vacuum line off the EGR would be good to determine if there is a bad EGR vacuum control solenoid. If it doesn't make a difference, though, the EGR may still be stuck open. The only way to really test that is to remove it all together and bolt on a plate.
Crane recommended 3.55 gears for my E303. I'm sure you are probably in the same boat.
Do you have a specific code reader or are you using jumpers? If one doesn't work, try the other.
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351W 89 Mustang GT Convertible