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3051S : HP steam flow transmitter saturating

Hi , all.

I am looking at the following phenomenon in my plant: this is a combined cycle running 2 GT's and 1 ST from Mitsubishi.The HRSG manufacturer is Vogt.

During a 2 on 1 configuration our HP steam flow is around 650 kpph at base load :294MW.The flow indication is consistent with the feed water flow.When we are in a 1 on 1 configuration , the flow is reading is fine until we reached 280MW on the GT where the flow becomes erratic and saturates. During this excursion , the DP and the pressure variables exceed 1070 psid and 1060 psi respectively. That throws our drum level control into single element also since our HP steam flow is saturating at the upper range value of 960 KPPH.
Our 3501S transmitters is ranged to 960 KPPH upper range. The only way to get out of this situation is to back down the GT load.Do we have to increase the transmitter range ? Any suggestions would be appreciated?

Thank you.