prostart remote control range poor

Ok here is my problem I have a prostart 3in1 alarm/starter/keyless in my 94 Jeep grand cherokee limited.  I replaced the battery in the remote thinking it was going bad been in there 3-4 years now.  I replaced it with the correct battery (duracell) not a cheapo china one.  The range is still poor like i have to put the remote almost next to the truck to unlock or remote start it.  Before I used to be able to remote start it down the block if I needed to.  Is there anything that might be causing this to happen as nothing has been changed in years to it.  Also i checked the battery with a multimeter and its perfect and the old battery is a little worse but still acceptable.  What could cause this been doing this for months now?  The antenna is mounted on the front window and has not been moved since I installed it years ago.