The J = 3 ← 2 transitions of CF 3H and CF 3D in the v 6 = 1 state have been observed and analyzed. Direct l-type resonance transitions have also been observed for the v 6 = 1 state of CF 3H from J = 19 through J = 32 and from J = 29 through J = 35 for CF 3D. In addition, splittings of the K = 3 transitions were observed which have been accounted for by including the l-type interaction, Δ l = 2, Δ K = −4, between the l = −1, K = 2 and l = 1, K = −2 levels. Their frequencies were analyzed by taking into account the (2,2), (2, −1), and (2, −4) interactions and some third-order terms. From the analysis the product q 6 l 6 was determined to be negative. Furthermore, two transitions of CF 3D, J = 34, K = 0 and 3, were found shifted by accidental degeneracy through an r-type interaction, and the analysis gave C 6 = 5662.0 ± 0.9 MHz, and the Coriolis coupling constant ζ 6 = −0.7524 ± 0.0003 for CF 3D and an improved value of ζ 6 = −0.8053 ± 0.0004 for CF 3H. The values of | q 6| and | r 6| were found to be 36.27917 ± 0.00013 and 0.97 ± 0.02 MHz for CF 3H, and 31.8465 ± 0.0003 and 1.297 ± 0.002 MHz for CF 3D. The three cubic constants k 666, k 466, and k 566 have been evaluated using the q 6 and r 6 values obtained for both molecules. Finally, certain unusual features of the Stark effect have been investigated; the unusually slow Stark effect observed for the Δ J = 0, K ≠ 3 transitions of CF 3D and “forbidden” Stark transitions which appear for quickly modulated lines in both CF 3D and CF 3H. Frequencies of the “forbidden” lines have been accounted for by introducing the ω-type interaction, Δ l = 0, Δ K = 6 between l = ±1, K = ⊣2 and l = ±1, K =±4 states, with differences in the upper and lower doublet splittings substantiated by rf/mw double resonance.