Gone to code "66" (flap system) and there you can mix in the correct amount of elevator trim needed. You may have to do a couple of flights to get it correct. If it is gaining altitude when you drop the gear it is usually a indication that you have too much speed when dropping the gear.

I'm assuming you are using the three position switch for flaps. On code 66 put the switch in the mid position (take off) and put in a couple of clicks of down elevator, then put the switch in the land position and put in a couple more clicks then try it out.

Are you using crow??