First off, lets work on your screenshots. To take a screenshot in game, simply press "Print Screen." When you exit your game, go into the NASCAR Racing 2003 folder and look for a .tga file that says something along the lines of NR03001.tga. That file is your screenshot. You won't be able to upload that here as a tga, so if you have a paint program that can convert tga's to a file that is shareable then use that, but if not you can use an online converter. Just type something like "convert tga to jpg" in your search engine and something should pop up.
Next, it is hard to tell exactly from the screenshot but the impression I am getting is that the main install mod looks good but the mods you have added don't look quite as "crisp." The most likely reason for this is that the cars themselves are set at a lower resolution. First of all, if a carfile is set at a lower resolution it can't be effectively brought up to a higher resolution, so if you have a car that is lorez, you are stuck with it. When you paint a car, the first option that effects resolution (i.e. the amount of pixels that are generated on screen) is the size of the template you are painting on. The game set standard is 1024 x 1024. This is "standard resolution," but since the days of "LoRez" 512 x 512 are basically gone, the standard is now generally referred to as LoRez. HiRez are considered to be templates that are 2048 x 2048. Basically, the larger the image, the more pixels get put on the model, the more "crisp" the image becomes. You can go hugher, such as 4096 x 4096, but the game can't really handle that. The second option that affects resolution of a carfile is how the image is applied to the carfile. The game uses a standard "put image on model" conversion, but another option is to download WinMip2 to add the template to the carfile. With this program, you can compress the file so that it uses less memory when rendering. This has a lesser effect than the image resolution, but it does degrade the "crispness" a little. The reason why files are compressed and sometimes smaller resolution templates are used is because some computers can't keep up with the amount of pixels being generated from all the cars, the track, the UI, and all the visual effects (smoke, shadows, tire marks, etc). Also keep in mind that some mods need more rendering power than the base mod because they have more detailed models. For example the MENCS19 mod is highly detailed and requires much more memory usage than the base model does, so concessions have to be made to make the game not slow down too much.