Finding you have the impulse to swim at faster tempos is common, really expected. This is due to removing unnecessary movements in recovery arm that have been eating up that time. Practice at the slower tempos by slowing the stroke cycle without extra recovery arm movements. Then discover faster tempos you can swim at that may have once felt impossible due to those added terrestrial movement patterns with recovery arm.
I had my squad do an asymmetric pyramid I think Joel mentioned in this post or another, running down to really fast tempos to clean up those lingering/added recovery arm destabilizing movements. Note this is a set is not for the novice or those new to TI and is intended for the intermediate and above swimmer that already has a good sense of balance, is swimming longer distances and may be stuck in a tempo plateau.
Leave out stroke count and just concentrate on what tempo(s) really click for you.
On 50's, starting at 1.2 tempo, descend .1 each 50 until you get to .8 or .7, i.e. 1.2, 1.1, 1.0, .9, .8. Just try your best to hit .8
Swim 3 x 50's at the fastest tempo, with plenty of rest between 50's so you can breathe on 4's.
Ascend up the ladder increase tempo 0.5 each 50. Keep going up (slowing tempo) until you reach a tempo that you can easily hold for that 50 and *feels* like everything is clicking given your wing-span/height, skill, and physiology that is personal to you.
Then bump it back down 0.5 (faster) and swim 5 x 100's. Now monitor your SPL and see what it actually is and it should be in the green-zone.
This is a good sweet spot to work from swimming faster or slower tempos depending on the distance you are swimming and which tempos/spl are sustainable. This will set will help two primary things, 1. clean up lingering movements preventing you from swimming at faster tempos, 2. discover the "true" tempo and SPL that just feels like it clicks and feels great for *you*. As a coach observing this process, you can easily see a tempo on swimmer that just is working and you can't help but say "wow - that's it, that's it!" and give the swimmer that feedback. Also as skill improves so will your sweet-spot tempo and SPL. Keep in mind, the lowest SPL is not the objective, rather find the right SPL and tempo that works for you.
Enjoy your tempo journey!