Loosing battery power

[cwest]

86' K20.  For a while now I've had a flickering battery gauge.  I took real notice when driving at night and all of the trucks lights dim randomly, sometimes to the point of no light at all.  I Googled it and the first thing that popped up was bad alternator, so I swapped in a new one, to which nothing changed, still flickering lights and battery gauge.  I jiggled every wire I can see looking for a short, but nothing.  The only thing I've found that distinctly causes a dim in lights is if I step on the rear passenger side bumper.  Does this still sound like a short somewhere, or is this something specific someone has dealt with?  It happens predominantly after the truck is up to temp as well.   

[bd]

How strong does the starter crank the motor?

It sounds like a connection problem... somewhere.

To begin, take a thorough look at the following:

• battery terminal and cable condition - realize that cable strands can corroded and break inside the cable jackets where hidden from view.  If you see green fuzz, replace the cables with at least 2-gauge all copper battery or welding cables.
  
  
• battery cable connections to the battery, starter and engine block or alternator bracket
  
  
• ALL of the remaining grounds (battery-to-radiator support, battery-to-frame, right rear cylinder head-to-cab, instrument panel-to-cab, rear lamps-to-bed sheetmetal, and bed-to-frame)
  
  
• tightness and condition of all wires connecting to the alternator
  
  
• condition and tightness of the fusible links at the starter solenoid and firewall junction block
  
  
• heavy-gauge red B+ feeds as they run through the conduit in the vicinity of the right exhaust manifold and up behind the engine, inspecting for burning and/or chafing
  
  
• heavy-gauge red B+ feeds where they pass through the firewall bulkhead connector, inspecting for heat stress and melting of the connector body
  
  
• the splice in the heavy-gauge B+ feeds taped into the harness under the dash near the fuse block (this one is a pain - save it for last)
  

[1967KaiserM715]

Double check grounds, battery to frame, frame to engine, and frame to cab. Sometimes these corrode internally too, so replacing to rule it out may be the best choice.

[cwest]

The starter turns the engine normally except about 1/10 starts it stutters for a half a second before cranking.  Having said that I'll probably start with the starter connections, and then the rest of those suggestions.  I'll you guys know, thanks for the replies