198°F isn't unusually hot for an 8L90, so I don't think temperature alone caused the issue.
Since everything returned to normal after the truck sat for several days, I'd be looking at an intermittent electronic or hydraulic control problem before assuming the transmission itself has failed.
The first thing I'd do is scan the Transmission Control Module (TCM), not just the ECM. GM transmissions can store manufacturer-specific or history codes that won't trigger a check engine light.
I'd check:
TCM history and pending DTCs
Commanded vs. actual gear
Line pressure
Shift solenoid status
Torque converter clutch (TCC) slip
Transmission fluid temperature
If it happens again, try to capture the data before cycling the ignition, since some intermittent faults disappear after a restart.
A professional scan tool that supports full GM transmission diagnostics makes this much easier. For example, the Foxwell NT809BT can access the TCM, read manufacturer-specific transmission codes, and display live transmission data that's not available on a basic OBD-II reader:
https://www.foxwelldiag.com/products/foxwell-nt809bt
Hopefully it's just an intermittent control issue, but I'd definitely pull the TCM data before replacing any parts.
The 92-95 SCPI spider injectors are notoriously problematic and hard to source new replacements. I’d pull the intake manifold first to inspect cracked lines and brittle plastic legs before dropping $350 on a rebuild. The 1.5 OBD system only offers limited data, no misfire tracking, which is normal for this 1995 model. Enjoy the project!
Yea a fluid change is in order here. Honestly, your transmission didn’t even get hot. During the summer in stop and go traffic I’ve seen my 8l80 get up to 216 and it was still shifting smoothly.
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