A wireless device, such as a user equipment device (UE), and a base station are disclosed, which may communicate with more efficient use of dynamic transmit time interval durations to enable a faster and more efficient ramp up of TCP communications to a higher or maximum throughput. The UE may communicate uplink or downlink communications with the base station according to a first shorter TTI duration for a first period of time. After the first period of time, the UE may communicate uplink or downlink communications to the base station according to a second longer TTI duration. For the case of uplink communications, the UE may be configured to increase a congestion window size after each acknowledgement of an uplink communication received by the base station during the first period of time. For the case of downlink communications, the base station may be configured to increase a congestion window size after each acknowledgement of a downlink communication received by the UE during the first period of time.