Mueller, 28, led Texas with 15 power-play goals during the regular season and ranked fourth on the team with 57 points (25 goals, 32 assists) in 60 regular-season games played. The native of West Seneca, N.Y., made his Stanley Cup Playoff debut with Dallas this postseason, recording two shots in four playoff games.
Mueller also appeared in nine regular season contests with Dallas in 2013-14, registering eight shots.
Jeffrey, 26, recorded four points (two goals, two assists) in 34 regular-season games for Dallas and Pittsburgh in 2013-14. The 6-foot-1, 205-pound forward earned 10 points (four goals, six assists) and a plus-6 rating in 21 regular-season games for Texas this year.
The native of Sarnia, Ont., was originally drafted by Pittsburgh in the sixth round (171st overall) of the 2007 NHL Draft and was claimed off waivers by Dallas on Nov. 17, 2013.