Recently replaced torque converter solenoid, now what.

Issue originally was hard shifting, ******** or not at all shifting unless releasing throttle peddle. Checked engine code, was PO741, torque converter ckt perf/stuck off. Replaced TCC. I thought vehicle was fixed, I was wrong, code is back. Although the trans is shifting way better than pre TCC install, only one occurrence that car actually stalled. Now at certain RPM's, and no specfic driving conditions, I can watch the tach fluxate between 1500-1700 RPM's. My question is what's next to check, another TCC maybe or torque converter? I am a mechanic by day and sometimes by night :) so if u feel the need that I should check line pressure or anything else plz let me know, and what the read out should be and I can do that. FYI, the TCC that I bought from advance seemed to have trans fluid residue on the new solenoid and packaging. I was hoping that the residue was from manufacture inspection, wishful thinking maybe? I wonder if I got someone's used solenoid. Thank you very much for your time and help!