There is nothing in the schematic that suggests boominess. I have built one, but deviated quite a bit from the BOM (and used a 12ax7). You could try another tube (or different type of tube) before you start desoldering/resoldering. If there is nothing wrong in your build, you still have an option to use cathode bypass caps ... (the distortion version leaves C15/C17 open). Lower cap values will increase treble content, so you could install sockets and experiment with values between 0.1 and 1 uF.