SIP-PM Exhausts - 15mph lost top end!

Have recently replaced my PM pipe for a SIP exhaust. I have a Malossi T5 with Dellorto carb & HP4 lightened flywheel, skimmed head etc, all set up on the Dyno-Jet by PM Tuning. With the PM I could easily reach 85mph but with the SIP Torque now fitted I struggle to reach 70mph. Acceleration has improved but that’s all. No adjustments/settings have been changed. Can anyone help?

The down pipe on the t5 torque version is doing its job. For more revs you need the shorter version of the down pipe,