mallory ignition problems

i have a 91 5.0 mustang that i insatled a mallory computer controled ignition. at first it worked great but later when i stayed at constant rpm it will sputter and miss and i really have no idea whats wrong. my friend had the same problem with his 88 truck and when he pulled the ignition it did the same thing and it lasted like 2 months. i was wondering if any one hade the same problem and what you do to fix it?
im positive that the ignition works correctly.
if any one has any info on what i could do to fix this i would appreciate it

Sounds like this new ignition may have a bad ground.:2cents:

my 87 f-150 is doing the same thing right now and i haven't figured it out yet. its really pissing me off. to top it off the starter went out on it today.