Mike I have my TX in front of me. I am going to run down my set up in hopes you can fix yours.
For starters I use CH-5 for the second elev servo. The closer the two servos are on the chanels the closer the initial movement of the two. First thing you need to do is in your menu go to BASIC (ACRO) screen (2/2) Go to *AUX-CH ---make CH5>NULL. This will let the gear chanel act normally. Otherwise it will only give full deflection one way or the other like retracts do.
Then go to ADVANCE(ACRO) screen 1/2. Pick a mix here. I use three because I have my spoileron mix on one and two. I like to set the second page up first so go to it. It should read as follows from the **bottom** up. POSI>NULL----SW>H it does not matter what switch.------TRIM>ON------LINK>OFF I also don't thinks this matters for this mix------SLV>GEAR------MAS>ELEV-----MIX>ON. Now on page 1/2 set both your rates on + or - 100% depending on how your servos are set. The offset should be 0%.
This should fix your problem. Unless you have a bunch of sub trim in one of your servo. This can keep it from giving full deflection.

Let me know how you make out.
David