i'm assuming you mean the patient had increased knee flexion in midstance (more or less) phase.....
considering that the gastrocs are a flexor of the knee, i'm not quite clear how increasing the strength of them would decrease the knee flexion...
what i have found to be rather appropriate in cases of increased knee flexion in midstance on the hemi-side is to use aggressive PNF extension patterns on the lower extremity...
now what may have occurred in your case is that bouncing on the trampoline and jumping on flat ground probably inadvertently strengthened the quads, which clearly act to decrease knee flexion in midstance...
though if you can explain HOW increased strength of the gastrocs led to decreased knee flexion, i'd like to hear it...

and you were probably very correct to address the pelvis rotation issue, but i usually find that hyperextension of the knee in midstance is associated with posterior pelvic tilt as well as hyperactivity of the plantarflexors...

congrats on making me turn around on my snarky comments and post something of actual substance...