It is not uncommon for the uplink buffers of cellular data networks to be saturated when the uplink bandwidths are low. This can cause the ACK packets for a downlink TCP flow to be severely delayed. Since existing TCP implementations are ACK-clocked, the downstream flow will suffer significant degradation, causing the downlink to be under-utilized. We present a new TCP variant, called TCP Receiver-Rate Estimation (TCP-RRE), that addresses this problem directly by eliminating ACK clocking. Instead, it uses TCP timestamps to estimate the receiving rate at the receiver, which it then uses to determine the sending rate. We show that TCP-RRE is able to improve download speeds by 2 to 4 times compared to existing TCP variants in both simulation and on real commercial cellular data networks. Our solution is practical because it is compatible with existing TCP implementations, requires no modifications to existing mobile devices, and is thus immediately deployable in existing ISP proxies.