Just had my 700R4 in by 88 Firebird rebuild by a shop, they said that the torque converter clutch went out and sent material through the transmission so they did a full rebuild with a new converter. Ive been driving it for about 3 weeks with no issues, took it in earlier this week for a post break-in inspection to make sure its all good. The day after they inspected it the speedometer and tachometer started intermittently reading random numbers. speedo would read 120 in 3rd gear with the Tach at the correct rpm, and the rpms would randomly read from 500-2000 while idling without the engine changing speed. At the same time as the cluster started acting up the converter started to lock up in 2nd 3rd and overdrive, causing the car to jerk on acceleration randomly, but it drives fine cruising and the issue is very intermittent

I have had an issue with the ICM before where the tach did something similar but from what I know that's completely unrelated to the speedometer and transmission lockup. Im planning on taking the car to the transmission shop because it does have a warranty but was wondering if all of those issues are related or not.