The backpressure routing and scheduling, with throughput-optimal operation guarantee, is a promising technique to improve throughput over wireless multi-hop networks. Although the backpressure framework is conceptually viewed as layered, the decisions of routing and scheduling are made jointly, which imposes several challenges in practice. We present Diff-Max, an approach that separates routing and scheduling and has three strengths: (i) Diff-Max improves throughput significantly, (ii) the separation of routing and scheduling makes practical implementation easier by minimizing cross-layer operations; i.e., routing is implemented in the network layer and scheduling is implemented in the link layer, and (iii) the separation of routing and scheduling leads to modularity.