Truck starts and idles then when put into gear sputters and stalls.

The windshield leaking is only a concern if the water is getting into the fuse box. If it is, resolve this first regardless. As far the sputtering and stalling - it sounds more like a concern with engine performance such as fuel and air mixtures. Seek local diagnostic guidance to resolve. Use this link to find some shops near you that can help with your concern: www.repairpal.com/repair-shops