Power Lock ?brain? under dash??

[bkk7791]

I have a 2002 F350 CC 4x4, with 59,000 miles. PRISTINE condition, and pampered.
Question for you guys...A while back, the remote starting acting like the battery in it was going dead...I would have to get closer and closer to the truck before it would unlock the doors...So finally I replaced the battery, AFTER it completely stoppped working. WELL...it STILL does NOT work at all.
The switch inside still locks/unlocks like normal, but it kinda seems a little sluggish when its doing its things..but it still works. I asked a trustworthy mechanic what he thought it might be, and he immediately said it was probably the "brain box" under the dash..like it was either the WHOLE box, or a module IN the box....
Does anyone know anything about this? Ever run into this problem? I am very good with my tools, and am sure can fix/replace whatever needs to be done, just don't want to start replacing stuff for the sake of it...

Any suggestions?

Thanks!!

BKK