Unfortunately, for your case, the Spring Reverb always seems to respond to tap tempo both with Tempo Mode ON and OFF. I don’t believe there is a way to set the tremolo speed only. Of course, if you only want to use the tremolo, you can turn the reverb out by turning the MIx all the way down.
That’s what I figured. I kind of found my own way around the timing issue by maxing out the decay time at 10bars [or whatever the max value is]. This decay time is long enough that when the tempo is changed, the decay is still long enough to sound pretty close to my old Super Reverb’s reverb tank.