What are the reference ranges with the FT4 and FT3 as they vary lab to lab.
My initial reaction is that if the ranges are close to what we often see. Your FT4 would be a little above the middle of the range. However your FT3 levels would be low. Which would indicate a conversion problem.
NDT has a lot more T3 in it than T4 only treatment. So directionally geting more T3 is I think the right direction.
I personally would probably since you are fairly close to ideal with your FT4 levels would only have recommended that you start adding a small dose of Synthetic T3, rather than switch horses completely to an entirely new medication. If you already have not made the switch to NDT, you may want to talk to your Dr about simply adding in some T3 (Cytomel).
To add support for your Dr, you can say that this is only making a single small change. And then you can monitor your FT4 levels with the T4 medication and monitor your FT3 levels with the ddosage of the T3 medication. Your Dr MAY be more comfortable with this rather than what appears to be a complete "unknown" for your Dr with the switch to NDT.
Just something for you to consider.
Also it might help that these were my labs from last week: TSH- 3.59; Free T4- 1.4; Free T3- 2.8