Help tweak my treble control, too bright 
 

Tom, working on one of those Fender PCB amps can be tedious because, unless I am mistaken (never seen one of yours inside) they are hard to get to the component side of the board. However, here is an approach you can try that will always work.
 
Regardless of what amp you're working on, there will be a volume control, and in this case a master volume control for the lead channels, right? Assuming that is the case, you can try putting a small capacitor between the two end lugs of that pot. Of course, in the case of PCB-mounted pots, you may need to get crafty to do this. 
 
This is what I would suggest: start with something like a .001uF cap and try that. Kills too much high end and gets too compressed? Back off a bit, say 560 pF... etc. The "best" approach would be to temporarily connect a pot, wired as a variable resistor and a cap between the two end lugs of the master volume pot. That way, you can "dial in" the amount of treble cut you want. Once you dial in the treble cut pot just right, measure the resistance and try placing the series of the cap you selected and the measument in the pot and substitute a fixed resistor instead of the pot. If your master volume is 1 Meg, you can start trying with a 1Meg pot and a .001uF (1,000pF) capacitor.
 
If your master volume pot is say 500K, try a 500K pot and a .002uF capacitor, etc. I think you get an idea of the scaling I am referring to.
 
Again, this will always work, but doing this has a tendency to make the amp sound compressed real quick if you go overboard. I strongly suggest you try the amp at the volumes you will be using it. Sometimes we dial an amp to sound "perfect" at home, and then you take it to a gig and it sounds muffled, compressed and lifeless. I always go for a little brighter than sounds right at first. High frequencies tend to get lost in a band mix, but once you've wiped them out, there is no way to bring them back to life.
 
Also note that if the problem with your amp is actually lack of bass, which may be perceived as excessive treble, it will be hard to make the amp sound right by eliminating high end.
 
Goo luck,
 
Gil