This can strongly be due to the Carrier oems the person that is cooking the rom is using, lets say he uses official sprint carrier oem, then it should have all the regular sprint configuration, and show same signal with airave as the stock rom, but if the chef has a Generic carrier oem then it is build to work with all the cdma carriers settings so it might be off by a little or more with airave, but still should not effect the performance of it.
Try installing this on a custom rom your using, and then reset, and see if it makes any difference or still the same.
http://www.jbawireless.com/Sprint%20...2020090109.cab