For your GM Chevrolet GMC CK Truck (Full Size) from 1988-1994, the Infinity Reference REF-6432cfx speakers would be a great factory speaker upgrade option. Here are the key features of these speakers:

- Reference Series 4"x6" 2-way car speakers.

- Plus One+ polypropylene woofer cone with hi-roll rubber surround for improved bass response.

- 1/2" balanced textile dome tweeter for accurate and detailed high-frequency reproduction.

- True Four Ohm Impedance technology, where the speaker's 3-ohm impedance combines with the speaker wire impedance for a 4-ohm load.

- Can handle up to 45 watts RMS (135 watts peak power) for a dynamic and powerful sound experience.

- Wide frequency response of 75-21,000 Hz to cover a broad range of audio.

- High sensitivity of 92 dB for efficient sound reproduction.

- Compact top-mount depth of 1-3/4" for easy installation in your vehicle.

Please note that grilles are not included with these speakers.

Additionally, the package includes 2 pairs of speakers and 2 pairs of speaker connectors, which consist of the Speaker Harness and 2-Pin Flat Speaker Connector. These connectors are designed to fit perfectly with your GM truck without requiring any modification. They allow you to retain the factory speaker connectors while installing the new set of speakers, eliminating the need to splice the factory wiring.

Ensure that these speakers and connectors are compatible with your specific GM Chevrolet GMC CK Truck model and year before making a purchase.