How to clear my ecm on a 95 Chevy 3500 454 - 3500 Chevrolet Cars & Trucks

Check this forum.

https://blazerforum.com/forum/2nd-gen-s-series-1995-2005-tech-41/ecm-pcm-fuse-location-95-blazer-72095/

The correct way is probably take to a dealer.
here is a link from impala forum which has the same thought as you, reset ecm.
https://www.impalaforums.com/chevy-impala-8th-gen-discussion/376818-how-to-reset-ecm-and-tcm-in-2012-impala.html

If you clear code and the problem continues it will come back if the car truly has a problem.

it will run very well on 91
it is not a high performance engine so 95 can be a waste of cash at the bowser
however it is your choice to what you use as the ECM will adjust to the rating
Just stay clear of e-mix fuels

DTC P0700: Transmission Control Module (TCM) Requested MIL Illumination
DTC P0700 can not be cleared from the ECM until the related TCM codes have been cleared.

The transmission control module (TCM) uses the (GMLAN) to signal the engine control module (ECM) that the TCM is requesting malfunction indicator lamp (MIL) illumination. This happens when the TCM has determined that a failure affecting emissions has occurred in transmission control system. When the ECM receives the a message from the TCM, DTC P0700 will set.
You don't say which engine your's has ! Or which transmission .
Automatic Transmission - 4L60-E/4L65-E/4L70-E

You need to have TCM checked for codes .

POSSIBLE CAUSES FOR THAT CODE OF A CHEVY ARE:
WEAK BATTERY
FAULTY COMPUTER OR ECM (Engine Control Module)
BLOWN ECM FUSE
ECM WIRE HARNESS IS OPEN OR SHORTED
ECM CIRCUIT HAS POOR ELECTRICAL CONNECTION.

It sounds like your starter is wearing out. You can have it rebuilt, or you can have it replaced. I would also check the oil level, just in case.

I’m happy to help further over the phone at https://www.6ya.com/expert/jeremy_69f3cc28d95bf514

Are you sure that it is an OBD 11 system not all of the 95s were It might have the 19 pin port connector but its not connected to anything and its an OBD 1 system a 4.3 they should be talking about a VCM not an ECM. Im not saying this is the olny possible answer you should check this out first . 96 was the first year year for OBD 11 AND SOME 95 DO HAVE IT

Pull the ecm fuse or disconnect the battery, for at least 10 minutes.That will clear all stored trouble codes.

You certainly have changed a lot of parts on this engine. Do you presently have any codes on it?

a 95 system differs from a 96 and above i would not recomend it due to emissions and many other functions