New Key Fob Won't Program

I wanted a second key fob for the newsed '99 Tahoe. Ordered one with the same part # as the original fob; the original fob has 3 buttons, the new one adds a fourth panic button. I can't get the new one to program. Sent one back as defective, the replacement won't program either. I'm setting programming mode by jumping 4 & 8 on the OBDII port. Locks respond indicating programming mode. The old fob programs just fine after ~15sec, but the new fob won't.
I've tried the new fob first, and also tried the old fob first; no difference, the new fob won't program.
Are there issues with the 4-button vs 3-button fobs even though they have the same part numbers?

I've had several issues with aftermarket fobs, even though they have the correct part numbers, not programing. The correct fob should match the old one excatly. When folks come in with one that they got online and they don't program, I sell them a new GM one and they program without a problem.

Hey Jeff, after doing a little digging, they offered two fobs for the '99. A "base" fob, with three buttons, which program the way you are doing it, and a "luxury" fob, with 4 buttons. The "luxury" fob with the panic button uses a diffeent proceedure requiring the disabling of the theft system. Basically, they are sending you the wrong fob...need the 3 button one. Say "Hi" to Jules!!!

Thanks Tim!!
Will do!