Do FAA sectional charts show all power/transmission lines?
From the FAA's Chart Users' Guide:


  AeroNav Products’ charts are prepared in accordance with
  specifications of the Interagency Air Cartographic Committee (IACC)
  and are approved by representatives of the Federal Aviation
  Administration (FAA) and the Department of Defense  (DoD).


Book 2 of the IACC Specifications covers Sectionals and VFR Terminal Charts and provides the following guidance for transmission lines:


  3.6.6.3 Telecommunication and Power Transmission Lines (T-Lines)  
  
  3.6.6.3.1 Landmark Value  
  
  T-Lines, if depicted on charts, are shown primarily for their landmark
  value. Determination of whether a T-line has landmark value or what
  constitutes chart congestion are matters of FAA Flight Edit judgment.
  Flight Edit shall either delete or add T-Lines on the Flight Edit
  Standard. T-lines with landmark value should be shown in open country
  and not in congested or built-up areas. Through open country, T-lines
  should be shown as continuous lines, interrupted only for reasons of
  cartographic practices. Location of the pylon symbol is dependent 
  upon the length of the T-line; approximately at 1" intervals on a line
  3" or less in length, and approximately 2" apart on lines longer than
  3".


The transmission lines may also be charted under the rules of section 3.9.8.6 Obstructions.  

So, no. T-Lines are not charted exhaustively. They are charted only when they have landmark value or are charted as an obstruction.