Throttle body would have absolutely nothing to do with very slow cranking, so skip that IMHO.
Sounds like a voltage/ground problem to me.
Before starting it, check the battery voltage.
While starting it, have someone check the voltage at the starter motor.
If the voltage is all good, get the starter motor checked.
Another quick test to see whether low voltage is causing issues, before starting it, hook up another rig to it and use jumper cables as well as your own battery. See how it cranks and runs doing that.
On some rigs, when voltage is low, the engine ecm relearns everything when first started with low voltage. Thus the rough running issues. This coupled with a lethargic starter motor leads me to believe there are still indeed voltage issues. Also go over all ground connections and check for voltage loss there too.
Hell, our 98 XJ does it when it sits so long the battery goes dead, then we have to jump it from the charger/starter pack to get it going. Got to keep the gas pedal down a bit or it would die. After a minute or two, it's perfectly normal again.
1998 XJ on 37's.JK Rubi axles with chromo shafts and ctm's, 4:1 transfer case, etc etc etc.The Cherylkee....
2003 Range Rover HSE, 4.4 Quad Cam.
1998 Range Rover 4.6 HSE
2000 4.7 4WD WJ with a rebuilt motor.
4.3/700r4/new frame buildup (YJ)....
Years to gain the hands on experience, and offer it freely.
Minutes to gain the knowledge from the internet, and quote it just as freely.