Right now a trade route importing tech from a foundation will default to raising the uplifted planet to the foundation's TL. Foundations usually have higher TL than most planets need and each tech trade route must be reconfigured manually to prevent over-teching. I suggest that the player be prompted to specify the desired TL at the time that they create the tech trade route.
An alternative would be to rejigger the way TL is assigned, to allow the user to specify the desired TL of a planet from the planet interface rather than a trade route. Let the game then automatically build a project or establish a trade route depending on whether there is a foundation in the vicinity. This could also give planets extra resiliency through the ability to auto-build projects (up to TL 7) to maintain TL if a foundation trade route is disrupted due to a war or civil war.