With the rapid growth in the number of Internet users and abundant network application, there is an increasing demand for network bandwidth. Optical fiber networks provide increased bandwidth capacity which makes them the preferred choice for huge data transfer operations. Improved network capacity management becomes essential for addressing congestion complications that impact extensive networks specifically those implemented underwater. The Transmission Control Protocol (TCP) needs improvements because it functions as a reliable connection-oriented protocol to boost data transmission performance. SACK TCP is typically used in a wide area network and will often demonstrate significant congestion and resulting packet loss due to the single round-trip duration period and its slow-start phase with large congestion windows. An optional technique called LSS can be used to enhance network performance during periods of high congestion by expanding the congestion window size as it expands during slow-start operations. In high-rate networks, LSS does not take full advantage of the potential bandwidth gain and leads to low efficiency. In this paper, we investigate a method referred as Limited Slow-Start Modification 2 to improve congestion control performance. The technique operates by rapidly growing the congestion window possibly doubling it for each received ACK and initially three times as more bandwidth will be used per cycle. So, the data flows more efficiently, even at high-speed networks and stable connections. This paper simulates and analyzes the performance of SSM2, SACK TCP with LSS, regular SACK TCP over various high-speed network scenarios. SACK TCP LSSM2 significantly increases the network-speed with making use of existed bandwidth resources and very small congestion. The study has shown remarkable enhancement of the performance of TCP in modern high speed networks.