I agree with Chris.. Check the thickness of the needle you are using... They can vary greatly. IToo thick a needle could easily spread the muscle fibers too far apart and make it difficult to close the gap to a less noticeable level as the internal temp is raised.
Lonestar 24" Vertical offset w/ Insulated Firebox & Performer Platinum
Former owner: Jambo Backyard, Klose BYC, Med. Spicewine, Pitts & Spitts, XL & (2) Med. BGE's, 22" WSM & (2) 18" WSM's, 18" & 22" Weber Kettles