Mine will set, accel, decel and shut off. But it will only hold speed for 2 to 10 minutes. Then it drops out or it mimics running out of fuel until I shut it off.
I bought a replacement amp from a forum member, but it did not work at all. He is sending me another one. I sent an email to Peter at GDL and described the symptoms. Peter was pretty sure that since the actuator worked properly when it was on, that the problem was with the amp. He suggested I try another one.
If the replacement amp does not work. I am done and will spend the $185 for the Audiovox unit.
When you soldered the kit wires to the terminal strip in the old amp, did you do that so you didn't have to splice wires into your stock wiring harness?

__________________
1987 300D 146K Original #14 Head
One eye on the road, the other on the temp. gauge

Gone But Not Forgotten
1983 380 SEL Long gone
1983 300SD Wish I hadn't traded it in on a 90' Corvette
1989 300SE My all time favorite
1995 E420 Went like a bullet