Hello,
Web/HTTP and TruClient are different protocols. The transactions in TruClient can measure other things than network round-trip as in Web/HTTP.
You need to specify the End Event of the transaction in TruClient so it will measure the desired time.
Additionally, the mechanisms are different. While web/HTTP measures the raw network level, TruClient is much more closer to the user and coupled with the browser, times may be different after all.
Hope it is clearer.