Loss of power in 6th gear, new turbo

[Littleharoldeh]

   So old turbo was going. Oil getting by seal and no boost so got another, not gonna lie jobber. Tha being said, first few drives was all good, tons of power no more oil leaking on the garage floor life is good. Now got pretty cold here in Canada, noticed the other day it just didn’t seem to wanna stay in 6th gear long. The turbo working cause I can get up to 100-120 fast and easily,  but once it gets to 6th gear say 110 kph, you try hold it there but it just slowly creeps down then shifts back to 5th, not really economical always in 5th.  Where should I start looking? Thanks in advance 

 

I forgot to mention, last week when I first notice it acting up, I notice it almost so put tearing a bit higher rev, so when I stopped I revered her out in neutral and it sputtered and was very smoky. 

Edited December 8, 2025 by Littleharoldeh