RPM tops out at 2100 in neutral, park or in gear and won't shift

[Vernsmith2017]

My 2007 Topkick with an 8.1L gas engine ran fine when I parked it Wednesday. Yesterday it wouldn't rev over 2100 except when I let off the gas sometimes it would jump to 3000 and right back down to 900. Called my mechanic who said it was the cat converters clogged. Did a field repair with a sawzall but nope, same issue. Any ideas?

[KARNUT]

My 2007 Topkick with an 8.1L gas engine ran fine when I parked it Wednesday. Yesterday it wouldn't rev over 2100 except when I let off the gas sometimes it would jump to 3000 and right back down to 900. Called my mechanic who said it was the cat converters clogged. Did a field repair with a sawzall but nope, same issue. Any ideas?

You didn’t say if you changed the fuel filter. Depending on year you can’t rev high rpms in neutral. When you drive it without a load if you go easy on the accelerator will it shift? My first guess would have been cats.


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[Vernsmith2017]

We're trying that next but won't be til Monday when NAPA opens. Thanks!

[newdude]

Any codes or check engine lights?

[Salvatore Astuto]

Do you have a PTO? If the PTO is engaged, it will limit RPMs and not shift