I assume you only disconnected the negative side of the battery, or at least disconnected it first and reconnected it last?

I ask that because I have seen people mess up on that part and fry the fusible links on the positive side creating exactly this problem.

If that was okay, I would strongly suspect the terminals and the battery cables being corroded on a car that old. Sure they were working fine, but flexing them could weaken old cables. Do a voltage drop test between the starter and battery with both positive and negative side. Find out how far the power is going before it drops.

Rx8 problems?

2007 mazda rx8 new spark plugs new starter new rear o2 sensor when scanned it brings up the rear o2 sensor and spark plugs even though they are new Cant Floor My Rx8 Have To Baby The Gas Petal To Get Moving Recently The sweet Spot So To Speak Has Gotten Smaller And Smaller Where I Just Stutter Along Untill I Catch Speed Any Idea Of Whats Wrong?

1: your rotors are warped
2: An issue with the antilock break system
3: You are breaking to hard and invoking the antilock system

Most likely #1. They can probably pull the rotors off and machine them. About $150-$200 I would expect.