Lincoln/Mercury Repair: cranks slow when warm, starter solenoid, battery cables

Question
My 89 Lincoln cranks slow (almost like a dead battery ) but only when warmed up. I have replaced the starter, starter solenoid and the battery checks good. Timing is in spec. This is making me crazy. Any advice you can offer will be greatly appreciated. Thank you!

Answer
definitely cables. i have seen it many times. replace the battery cables, both pos. and neg. and the cable from the solenoid to the starter. the solinoid system is so prone to faults that i usually add a cable from the bolt that holds the starter up to the same bolt that goes into the fromt for the block ground. this will make a good starter last longer too.