You probably don't need to gain weight very quickly to keep your strength going up. TM or similar will be a nice change of pace for you. What I would do is make sure you're not doing just 3x3 on any of the lifts anymore, since it's not enough volume to drive your strength up, likely, at this point.
I would probably be trying to gain 1-2lbs a month and keep an eye on your waist.