..... I can't hear high notes, they just blend in and you can't hear them..
Start by putting your amp to your ears level or tilt it so it shoots straight at your head. (ears)
+10
If you ever change rigs, try two 2x10 and stacking them vertically. There are many threads on TB about this. Note only will you hear yourself better, you'll get better dispersion. Cabs where the speakers are not vertically stacked create cancellations of mid/high frequencies. Bill Fitzmaurice expounds on this topic in many TB threads.
The sound man claims it's fine out in the audience.
There's a big difference between hearing yourself on stage and FOH. If the sound guy says it's fine FOH, then it is.
I've thought about buying a wireless and playing out in a back pew at practice to hear how it sounds.
That's a good idea for any type of gig.
You can try raising the pickup on the D and G side if they are actually out of balance.
I looked up your amp's specs:
* 2 x 500 watts of power, 1000 watts bridged mono
* Classic 12AX7 High Voltage Class-A tube preamp circuit
* Bass and Treble Shelving, plus mid-peak EQ controls
* Selectable brite switch for added high frequency response
* Selectable limiter switch with LED indicator
Since it has two power amps, you could set up a small bass cab in front of you and use it to monitor yourself. Your head has a balance control for individual cab volume. Or maybe stack another cab on top of it.
IMO, tilting your cab and directing the sound to your cranium would be the easiest (and cheapest) to test. The further you can stand in front of your cab, the better. Possibly try moving to different positions (from side to side) on the stage to see if that helps.