lost range on my 791vx

I have a 2003 nissan frontier (diesel). I usually park in an open car park and usually warm up the engine before reaching to the vehicle which is about 400-500 feet away from me. I usually get range just outside my office but now i have to go about 50 feet close to the vehicle to get range. The only thing i did was installed an audio amplifier and the signal and power cables are installed away from the antenna and alarm module. What went wrong? I did nothing to the alarm during the amp install, didn't even go close to it."I'm So Loud It Hertz"

This might seem obvious, but is the battery in the remote low?I'm not a professional installer. But I did stay at a Holiday Inn Express.

The battery is good. I use rechargeable batteries that when they get weak they suddenly go completly dead and never get a chance to run weak. And i have even used with alkaline batteries the range doesn't diminish when the battery is weak."I'm So Loud It Hertz"

did you move the antenna for the alarm?

Nothing was touched or moved in the alarm. Just installed an amp"I'm So Loud It Hertz"