It could be the antenna connector that needs to be resoldered.
The J401 are streaming the datasignalling to the RF board to set gain and frequencies and everything and I belive it is not a constant bad sensitivity when that happens, it will be all sorts of odd behaviour with slow scanning when the data to the RF board are interupted and the response from the RF board to the CPU board doesn't reach it's target.
Try to wiggle the antenna while monitoring to see if the signal strenght changes.
It could also be a component failure in the preamplifier, some users have reported that Uniden changed a transistor when they had bad sensitivity.
/Ubbe