L 3350 slugish modulator valve

[john16066]

I have a transmission problem when you put it in to forward or reverse it starts to go but slowly takes about 3 seconds then picks up to full power.
I put a gauge on the modulator valve its about 60 psi when you put it in gear then takes about 3 seconds till it jumps up to 250 psi .
Any ideas what the problem is