A retransmit value of 7.5% may not be too high by all standards, but depending on your network infrastucture may be indicative of a problem. You stated having decreased performance using the Telnet, have you compared retransmit values using another protocol such as ftp? Is your problem related to a specific device or all devices attached to your network? A specific time of day? Does it occurr internally or outside of your network? Do you telnet accross a router?
These are a few questions you may want to answer first in troubleshooting this issue. You may find that 7.5% is an expected value or you may uncover a bottleneck.