Mark
IMHO the pressure switch on the pump is set to what the pump is designed to deliver unless it has been adjusted.
We have Shurflo pumps which have a factory setting of 100 psi. You are using a pump to force water through a microbore hose and requiring it to do more than it was designed to do if your pressure switch setting is correctly set. Years ago, Shurflo pumps weren't guaranteed if we used them with mini or microbore hose as we were overloading them according to the manufacturers.
First stop for me would be to buy a water test pressure gauge and check what pressure the pump's switch cuts out at.
Whilst waiting for that to arrive, I might disconnect the pumps pressure switch and let the controllers dead end feature take full control. I would then try to increase the pressure gradually but monitor it. The Varistream controllers we use were designed to replace the pressure switch on the pump. Spring did say leave the pressure switch connected as 'additional protection'.
We certainly can't use our Shurflo pumps running flat out through minibore hose so it would be even less likely that you would be able to do it with microbore.
We have also found that as we increase motor speed and hence water flow at the brush head, our motor's amp draw also increases quite dramatically. (Varistream = -+ 1 amp for each point of flow increase ie 3, 4, 5 & 6 in this range.)
If the pressure switch cycles (on and off rapidly) then the contacts will burn out. I think the Shurflo pumps were especially vunerable with this.