Once you have legitimate PSP game files, configuring PPSSPP properly ensures the best possible experience:

The health bar, radar, and fonts are altered to look exactly like GTA IV.

Features Toni Cipriani in the 1998 version of Liberty City. It offers the same map layout as GTA III.

This article provides a comprehensive overview of GTA 4 for PSP, focusing on how enthusiasts created playable versions (ISO/ROM) and where to find high-quality, high-compression downloads, while acknowledging the unofficial nature of these mods. GTA 4 PSP ISO ROM High Quality Download: A Complete Guide

Turn off or set to xBRZ to prevent performance bottlenecks. Safety and Security Tips

No legitimate mod exists that transforms PSP hardware or emulated PSP games into GTA 4. The closest you'll find are texture mods for the PC version that replace certain elements (like replacing the in-game phone with a PSP model), but these don't allow the game to run on PSP hardware.