Re: ED Slack in accelerator cable / TPS
Firstly, I think your car would always take off in 1st from a standing start, even with your foot off the accelerator! The only time it will take off in a gear other than 1st is if it is in Limp Home Mode (3rd gear & reverse only).
Secondly, I doubt it will be the accelerator cable as a stretched one will merely not have enough "pull" in it to fully open the throttle body when you floor it (and it won't be as responsive compared to a new accelerator cable).
Thirdly, it sounds like something electrical, from dodgy sensors (TPS? as you stated in your title), wires, to the ECU suffering from something. It could even be the tranny itself? Maybe taking it to a transmission or auto electrical specialist is the best bet.
Good luck with your ED!
'91 EB Fairmont Ghia V8.
Pacemaker PH4000 extractors
Meaty semi-twin system
AUII XR8 t/b & maf, ELGT snorkel
BA semi-manual shifter conversion
Electronic shift kit
4.11 Hydratrak LSD
Explorer intake manifold
Contra 16x9 rims, rubber: 225(f)/245(r)
Chiptorque HP2 chip
ET: 14.78 @ 91.48mph, 137rwkw!