I agree with willtravel - the top lowers when the lowering valve is opened, which sends the hydraulic fluid that is holding the top up back to the reservoir. There's no way to adjust the speed at which this happens, the valve is either open or closed. And, as he said, the manual lowering valve, if open, would keep the top from raising.
What do you mean by "lowering too hard"? There's nothing in the cable assembly that controls this. When lowering, the top should come down smoothly and rather quickly. I think mine drops fully in about 5 seconds.
Hi-Lo 1707T - Tire Minder TPMS on Tow Vehicle and Trailer, 300W Solar Battery Charger, Equal-i-zer WDH, Progressive Dynamics Converter, Fan-Tastic Fan
2014 F150 Platinum 4x4 3.5L EcoBoost SCrew